Webasto Dual Top ST 6 User manual

Installation Instructions
Dual Top ST 6
English

Table of Contents
29026389C II Dual Top ST 6
Table of Contents
1 Installation / Repair ............................ 3
2 General information............................ 3
3 Statutory Regulations governing install-
ation ................................................... 3
3.1 Excerpt from the regulations ECE-R 122 points 5 (Part I)
and Annex 7 for the installation of heaters ................ 4
4 Additional Safety Instructions............. 5
5 Installation example ........................... 6
6 Heater installation .............................. 7
6.1 General...................................................................... 7
6.2 Dual Top ST connections ...........................................7
6.3 Installation location ...................................................7
6.4 Connecting the wiring harness ..................................8
6.5 Installing the heater................................................... 8
6.6 Additional information for exterior installation........... 8
6.7 Additional information for interior installation ........... 8
7 Type label ......................................... 10
8 Hot water system ............................. 10
8.1 Installation information for submersible pump systems
............................................................................... 11
9 Hot air system................................... 12
9.1 Heating air intake .................................................... 12
9.2 Hot air distribution ..................................................13
10 Cooling air system ............................ 13
10.1 Installation............................................................... 13
11 Boiler drainage and pressure relief sys-
tem ................................................... 14
12 Fuel supply ....................................... 14
12.1 General.................................................................... 14
12.2 Fuel pump ............................................................... 14
12.3 Fuel extraction......................................................... 15
12.4 Fuel lines ................................................................. 16
12.5 Fuel filter ................................................................. 16
13 Combustion air supply ...................... 16
13.1 General.................................................................... 16
13.2 Combustion air intake line ....................................... 17
14 Exhaust system ................................. 17
14.1 General.................................................................... 17
14.2 Exhaust line ............................................................. 17
15 Electrical connections ....................... 19
15.1 Schematic connection diagrams............................... 19
15.2 Supply voltage connection....................................... 20
15.3 Interior temperature sensor .....................................20
15.4 Connection to manual control panel.........................20
15.5 Connection to programmable control panel..............21
16 Wiring diagrams ................................23
16.1 Legend for wiring diagrams ......................................24
17 Starting the heater for the first time
..........................................................24
18 Fault Message Output .......................24
18.1 Manual control panel................................................25
18.2 Programmable control panel.....................................26
19 Warranty and customer service .........29
20 Technical Data ...................................29
20.1 Fuel for the Dual Top ST ...........................................29
20.2 Technical data ..........................................................30
21 Declarations.......................................31
21.1 Drinking water conformity........................................31

Installation / Repair | 1
9026389C II Dual Top ST 6 3 / 32
1 Installation / Repair
The improper installation or repair of Webasto heating
and cooling systems can cause fire or lead to leakage of
deadly carbon monoxide. This can lead to serious injury or
death.
To install and repair Webasto cooling and heating systems
you need to have completed a Webasto training course
and have the appropriate technical documentation, special
tools and special equipment.
Installation and repair may ONLY be carried out by per-
sons trained and certified in a Webasto training course.
NEVER try to install or repair Webasto systems if you have
not completed a Webasto training course, you do not
have the necessary technical skills and you do not have
the technical documentation, tools and equipment avail-
able to make sure that you can complete the installation
and repair work properly.
Only use genuine Webasto parts.
2 General information
Technical documentation, training by Webasto, special tools
and equipment are required for the installation and repair of a
Dual Top ST 6 heater from Webasto. This installation instruc-
tion is also available in several other languages on the Dealer
Portal.
Only use genuine Webasto parts. Refer to the Webasto Spare
Parts List, the Air and water heaters accessory catalogue, and
the motorhome catalogue for more information.
The Dual Top ST is approved for the following applications:
– Caravans
– Motor homes
WARNING
The heater is used exclusively for comfort purposes.
Due to its installation, it must not become a safety-rel-
evant component for proper functioning of the vehicle.
CAUTION
Make sure to use fresh drinking water when filling the
water tank of the vehicle / boiler.
The heater complies with drinking water regulations.
(see chapter21.2, "Drinking water conformity" on page
31).
In the following text, the term ‘water’ is used.
3 Statutory Regulations
governing installation
Dual Top ST 6 heaters have been type-tested and approved in
accordance with the regulations ECE-R 10 (EMC) and ECE-R 122
(heaters).
Permit numbers see chapter20, "Technical Data" on page 29.
Installation is governed by the provisions in points 5 (Part 1) and
Annex 7 of Regulation ECE-R 122 above any other.
NOTE
The provisions of these regulations are binding within
the scope of EU Regulation 2018/858 and should also
be observed in countries where there are no special
regulations!
See also:
chapter3.1, "Excerpt from the regulations ECE-R 122
points 5 (Part I) and Annex 7 for the installation of heat-
ers" on page 4
CAUTION
Failure to observe the installation instructions and the
notes contained therein will lead to all liability being re-
fused by Webasto. The same applies if repairs are car-
ried out incorrectly or with the use of parts other than
genuine Webasto service parts. This will result in the in-
validation of the type approval for the heater and there-
fore of its homologation / type license.
The Dual Top ST 6 complies with all applicable standards for
this type of product. When installing the Dual Top ST 6 heaters
and related components, you must follow all local regulations,
such as:
n98/83/EC Quality of Drinking Water.
nDIN 2001-2 Drinking Water Supply.
nDVGW W 291 Cleaning and Disinfection.
Make sure that the legal requirements for fitting the heater are
not violated during installation, in particular with regard to its
location and the routing of the exhaust lines.
NOTE
You must comply with country-specific registration reg-
ulations.
For vehicles with an EU type approval, an entry is not
required in accordance with § 19 section 4 of appendix
VIII b of German StVZO.

3 | Statutory Regulations governing installation
4 / 32 9026389C II Dual Top ST 6
3.1 Excerpt from the regulations ECE-R
122 points 5 (Part I) and Annex 7
for the installation of heaters
Subject to paragraph 5.3.1.2, heaters shall be installed accord-
ing to the requirements of paragraph 5.3.
Requirement from ECE-R 122, point 5.3.1.1.
See eur-lex.europa.eu document 42010X0630(08) for more in-
formation.
Vehicles of category O having liquid fuel heaters are deemed to
comply with the requirements of paragraph 5.3.
Requirement from ECE-R 122, point 5.3.1.2.
See eur-lex.europa.eu document 42010X0630(08) for more in-
formation.
Body sections and any other components in the vicinity of the
heater must be protected from excessive heat and the possibil-
ity of fuel or oil contamination.
Requirement from ECE-R 122, point 5.3.2.1. See eur-
lex.europa.eu document 42010X0630(08) for more informa-
tion.
The heater shall not constitute a risk of fire, even in the case of
overheating. This requirement shall be deemed to be met if the
installation ensures an adequate distance to all parts and suit-
able ventilation, by the use of fire resistant materials or by the
use of heat shields.
Requirement from ECE-R 122, point 5.3.2.2. See eur-
lex.europa.eu document 42010X0630(08) for more informa-
tion.
In the case of M2 and M3 vehicles, the combustion heater must
not be positioned in the passenger compartment. However, an
installation in an effectively sealed envelope which also com-
plies with the conditions in paragraph 5.3.2.2 may be used.
Requirement from ECE-R 122, point 5.3.2.3.
See eur-lex.europa.eu document 42010X0630(08) for more in-
formation.
The label referred to in Annex 7, paragraph 4, or a duplicate,
must be positioned so that it can be easily read when the com-
bustion heater is installed in the vehicle.
Requirement from ECE-R 122, point 5.3.2.4. See eur-
lex.europa.eu document 42010X0630(08) for more informa-
tion.
Every reasonable precaution should be taken in positioning the
heater to minimize the risk of injury and damage to personal
property.
Requirement from ECE-R 122, point 5.3.2.5.
See eur-lex.europa.eu document 42010X0630(08) for more in-
formation.
The fuel filler must not be situated in the passenger compart-
ment and must be provided with an effective cap to prevent
fuel spillage.
Requirement from ECE-R 122, point 5.3.3.1. See eur-
lex.europa.eu document 42010X0630(08) for more informa-
tion.
In the case of liquid fuel heaters, where a supply separate from
that of the vehicle is provided,the type of fuel and its filler must
be clearly labelled.
Requirement from ECE-R 122, point 5.3.3.2. See eur-
lex.europa.eu document 42010X0630(08) for more informa-
tion.
A notice, indicating that the heater must be shut down before
refuelling, must be affixed to the filler neck of the vehicle. [...]
Requirement from ECE-R 122, point 5.3.3.3. See eur-
lex.europa.eu document 42010X0630(08) for more informa-
tion.
The exhaust outlet must be located so as to prevent emissions
from entering the vehicle through ventilators, heated air inlets
or opening windows.
Requirement from ECE-R 122, point 5.3.4.1.
See eur-lex.europa.eu document 42010X0630(08) for more in-
formation.
The air for the combustion chamber of the heater must not be
drawn from the passenger compartment of the vehicle.
Requirement from ECE-R 122, point 5.3.5.1.
See eur-lex.europa.eu document 42010X0630(08) for more in-
formation.
The air inlet must be so positioned or guarded that blocking by
rubbish or luggage is unlikely.
Requirement from ECE-R 122, point 5.3.5.2.
See eur-lex.europa.eu document 42010X0630(08) for more in-
formation.
The heating air supply may be fresh or recirculated air and
must be drawn from a clean area not likely to be contaminated
by exhaust fumes emitted either by the propulsion engine, the
combustion heater or any other vehicle source.
Requirement from ECE-R 122, point 5.3.6.1.
See eur-lex.europa.eu document 42010X0630(08) for more in-
formation.
The inlet duct must be protected by mesh or other suitable
means.
Requirement from ECE-R 122, point 5.3.6.2.
See eur-lex.europa.eu document 42010X0630(08) for more in-
formation.
Any ducting used to route the hot air through the vehicle must
be so positioned or protected that no injury or damage could
be caused if it were to be touched.
Requirement from ECE-R 122, point 5.3.7.1.
See eur-lex.europa.eu document 42010X0630(08) for more in-
formation.
The air outlet must be so positioned or guarded that blocking
by rubbish or luggage is unlikely.
Requirement from ECE-R 122, point 5.3.7.2.
See eur-lex.europa.eu document 42010X0630(08) for more in-
formation.
The heating system must be switched off automatically and the
supply of fuel must be stopped within five seconds when the
vehicle’s engine stops running. If a manual device is already ac-
tivated, the heating system can stay in operation.
Requirement from ECE-R 122, point 5.3.8.1.
See eur-lex.europa.eu document 42010X0630(08) for more in-
formation.
A clearly visible operating display in the operator’s field of view
must indicate whether the combustion heater is switched on or
off.
Requirement from ECE-R 122, Annex 7, point 7.1. See eur-
lex.europa.eu document 42010X0630(08) for more informa-
tion.

Additional Safety Instructions | 4
9026389C II Dual Top ST 6 5 / 32
4 Additional Safety
Instructions
nIf the Dual Top ST heater suffers any impact damage, for
example by falling onto the floor, you must return it to
Webasto for safety inspection/repair.
nYou must not paint or repaint the Dual Top heater in part
or completely.

5 | Installation example
6 / 32 9026389C II Dual Top ST 6
5 Installation example
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Fig.1
Number Description
1 Interior temperature sensor
2 Water lines
3 Dual Top ST Heater
4 Dual Top ST Cooling-air intake cover
5 Dual Top ST Rubber bellows
6 Combustion air intake silencer
7 Cooling air and drainage water drain
8 Exhaust silencer
9 Drinking water tank
10 Water pump
11 Fuel pump
12 Fuel tank connector
13 Fuel tank
14 Hot air ducts
15 Control panel

Heater installation | 6
9026389C II Dual Top ST 6 7 / 32
6 Heater installation
6.1 General
CAUTION
You must adhere to the regulations specified in
chapter3, "Statutory Regulations governing installa-
tion" on page 3.
CAUTION
You must not lift the Dual Top ST heater by the hot
air inlet! This offsets the hot air fan and causes the
fan to contact internal comonents.
NOTE
You must observe the installation details specified by
the manufacturer of your vehicle.
6.2 Dual Top ST connections
1 2 3 4 5 6
789101112
Fig.2
Number Description
1 Heating air inlet
2 Water inlet (cold)
3 Water outlet (hot)
4 Cooling air inlet
5 Housing cover with inlet interfaces
6 Opening for Dual Top ST electrical heater wiring har-
ness (Dual Top ST 8 only)
7 Housing cover with hot air outlet
8 Exhaust outlet
9 Drain hose of overpressure valve and electrical safety/
drainage valve
10 Cooling air outlet
11 Fuel inlet
12 Combustion air inlet
6.3 Installation location
Installation location
All sides of the heater must have a clearing of 0.8 in (20 mm)
or more.
nSpace requirement at sides > 0.8 in (20 mm)
nSpace above the heater > 0.8 in (20 mm)
nSpace requirement for air inlet > 7.8 in (200 mm)
nSpace requirement for hot air outlet > 6 in (150 mm)
nHeater Length 20.8 in (530 mm)
nHeater Width 13.9 (352 mm)
nHeater Height 10 in (256 mm)
13.9 in (352)20.9 in (530mm)
>7.9 in
(200 mm)
10 in
(256mm)
>20
1 2
Fig.3 Heater dimensions [mm]
Number Description
1 Housing cover with inlet interfaces
2 Housing cover with hot air outlet
CAUTION
All materials located in the immediate vicinity of the
heater must be heat-resistant > 212 ºF (100 °C).
Find a suitable location for the heater
nMake sure to have sufficient space at all sides of the heater.
See Fig. 3.
nThe heater must be secured in a location in the vehicle that
can withstand a weight of 81.6 lb (37 kg).
nAll parts must be above the water wading depth (as spe-
cified for your vehicle).
nThe heater must be removable.
nThe heater must be accessible and the housing cover with
the inlet interfaces removable.
Webasto recommends installing the heater on the exterior of
the vehicle to save space. See also chapter6.6, "Additional in-
formation for exterior installation" on page 8.
The information contained in chapter6.7, "Additional informa-
tion for interior installation" on page 8 must also be observed
for installation within the vehicle.
The installation location should always be protected against
splash water and possible soiling.
Orientation of the heater:
The heater must be mounted in a horizontal position (tolerance±
5º), with its exhaust and cooling air outlet pointing down-wards.
See Fig. 4.
+5° +5°
-5° -5°
Fig.4 Required installation position.
CAUTION
Make sure that after installation the casing of the
heater is not in contact with any parts of the vehicle
body. Make sure that all moving parts can move easily.
Failure to do so may result in the hot air fan, cooling air
fan or other part being blocked.
0.8 in
(20 mm)
0.8 in
(20 mm)
0.8 in
(20 mm)
5.9 in
(150 mm)

6 | Heater installation
8 / 32 9026389C II Dual Top ST 6
Fig.5 The heater casing must not touch the vehicle body.
6.4 Connecting the wiring harness
1
2
3
4
Fig.6 Removing the housing cover with inlet interfaces
Number Description
1 Housing cover with inlet interfaces
2 Fastening screws for housing cover with inlet inter-
faces
3 Opening for Dual Top ST wiring harness
4Opening for electric heater wiring harness
(Dual Top ST 8 only)
The wiring harness X11 (12-pin) is already connected to the
heater.
Fig.7 Connecting the Dual Top ST 8 wiring harness.
Fig.8 Connecting wiring harness Dual Top ST 6
6.5 Installing the heater
nThe heater is mounted on the load-bearing parts of the
vehicle frame using brackets and M8 T-bolts which are in-
tegrated in the heater guide rails.
n
n
To prevent breaks within the heater and noises, it is neces-
sary to use vibration dampers. The M8 T-bolts and nuts are
tightened with a torque of 16 to 18 lb-ft (22 to 25 Nm).
Mount the heaters, brackets and vibration dampers so that
the dampers are compressed by the weight of the heater.
nSee Webasto product catalogue for motorhomes for differ-
ent kinds of fixation brackets.
nUse a minimum of 4 fixation points.
nFixation of the heater only on the top or on one of the
sides is not sufficient.
See Fig. 9
Fig.9 Possible ways to mount the Dual Top ST
6.6 Additional information for exterior
installation
nSecure the heater in such a way that it will not become de-
tached from the vehicle in case the vibration dampers fail.
A basic application possibility for securing the Dual Top ST
(see Fig. 10) is included in the scope of delivery.
nTo minimize energy loss, Webasto recommend that the hot
air hoses which run outside the vehicle be insulated.
Fig.10
6.7 Additional information for interior
installation
CAUTION
Both the Dual Top ST heater and the hot air hoses must
be installed out of range of the vehicle occupants and
of parts which are not temperature-resistant, such as an
installation box or behind furniture, see Fig. 11).
u
u
The minimum distances to the heater must be com-
plied with. See also Fig. 3.
All materials in the immediate vicinity of the heater
must be heat-resistant > 212 ºF (100 °C).

Heater installation | 6
9026389C II Dual Top ST 6 9 / 32
ATTENTION
uYou must install the Dual Top ST heater in such a way
that no non-heat-resistant part can fall onto the heater
or block the air inlet or outlet.
uAccidental contact by the vehicle occupants must be
avoided.
uThe heater must be accessible when maintenance or
repairs are carried out.
uTo ensure uniform air circulation, a ventilation open-
ing of at least 39.4 in² (100 cm²) must be provided.
See also chapter9.1, "Heating air intake" on page 12.
H
B
L
Fig.11 Example of the installation box
Arrow: Bottom openings for exhaust gas, cooling air, combus-
tion air and water drainage. Bottom opening using cut-out for
foam seal.
L≥ 34.6 in (880 mm)
B≥ 15.4 in (392 mm)
H≥ 12 in (306 mm)
6.7.1 Sealing off of exhaust gas to outside
Exhaust gases must always be routed to the outside and must
never enter the passenger compartment. Also see chapter14,
"Exhaust system" on page 17, and chapter3, "Statutory Regu-
lations governing installation" on page 3, for requirements of
exhaust system.
CAUTION
Use the foam seal approved by Webasto to seal off the
heater, and the exhaust pipe in particular, to the out-
side (see Fig. 12). Webasto assumes no liability for de-
fects or damage resulting from the use of other materi-
als.
Fig.12 Webasto foam seal
1. Drill a hole with the size and spacing of the two sections in
the vehicle floor. You can use the seal as template for this
purpose.
2. Make sure that the heating is positioned with enough clear-
ance. After the installation, the heater position, or that of
the seal must not be changed.
3. Escaping exhaust gases can reach extremely high temperat-
ures, therefore you must use a temperature resistant seal-
ing compound (up to 194 ºF, 90 °C) to seal the floor.
When installing the heater, you must also make sure that you
meet the following requirements to seal off the outside:
nThe seal must be evenly compressed to 60 %. See Fig. 13.
It is advisable to use vibration dampers with a height of
1.2 in (30 mm) for this purpose.
nAfter the heater is installed the exhaust pipe must be at a
minimum distance of 1 in (25 mm) from the seal and the
vehicle floor. See Fig. 14.
60%
Fig.13 Compressing the seal
CAUTION
To secure the positioning of the foam seal over the en-
tire service life of the heater, the seal must be replaced
every time the heater is dismantled.
Fig.14 Distance of exhaust pipe from seal and vehicle floor
NOTE
To guarantee proper, secure positioning of the heater
and the foam seal, Webasto recommend that you use
the Dual Top Interior Installation Kit. Using the bottom
plate, you can only secure the heater in one position
and the foam seal is simultaneously compressed to the
proper dimension (see Fig. 15). If you are interested,
please contact your Webasto Service Centre.
Fig.15 Webasto interior installation kit

7 | Type label
10 / 32 9026389C II Dual Top ST 6
7 Type label
The type label must be positioned in such way that it cannot be
damaged and remains clearly readable after installing the heater
(otherwise, a duplicate type label must be applied in a highly
visible location or in the engine compartment next to the
vehicle type label).
Inapplicable years must be erased from the type label and only
the current year must be readable.
8 Hot water system
The Dual Top ST 6 complies with all applicable standards for
this type of product. When installing the Dual Top ST 6 heaters
and related components, you must follow all local regula-tions,
such as:
n98/83/EC Quality of Drinking Water.
nDIN 2001-2 Drinking Water Supply.
nDVGW W 291 Cleaning and Disinfection.
NOTE
During and after installation of the water system, you
must make sure that no dirt can enter the water circuit.
To avoid leaks you must use a 10 mm standard hose connector,
such as John Guest/ASP, to connect water lines or hoses to the
heater. The water pipes on the Dual Top ST are especially
equipped with grooves which enable you to properly secure and
easily remove the hose connectors if necessary.
nUse a thermostatic mixing valve if required.
nIf you are not using a quick connection system used, then
secure the lines at all connection points in such a way that
they can withstand the system pressure and are watertight.
nFasten the hoses in such a way that they cannot be dam-
aged, for example by using hose clips.
Fig.16
1 2 3 4 5 6 7
Fig.17
Number Description
1 Fresh drinking water tank of the vehicle
2 Water pump
3 Cold water pump
4 Water outlets
5 Optional thermostatic mixing valve
6 Hot water line
7 Dual Top ST heater
NOTE
The internal diameter of the hot water lines should be
at least 8 mm.
Always use hoses, which are resistant to pressure (at least 4 bar)
and hot water (194 ºF, 90 ºC).
To operate the heater you may use any sanitary water pump
that:
ncreates a pressure of up to 36 psi (2.5 bar).
ncloses when shut off.
nhas a minimum operating pressure of 14.5 psi (1 bar).
When using submersible pumps, observed the instructions from
chapter8.1, "Installation information for submersible pump sys-
tems" on page 11.
Avoid back-flow of water from the heater to the vehicle’s fresh
water tank. Use one-way valves if required.
If the hot water temperature needs to be limited at the water
outlets, optionally use a thermostatic mixing valve (see Fig. 16).
If you connect to a central water supply (rural or city mains) or a
more powerful water pump, then you must always install a
pressure reduction valve to prevent a pressure above 36 psi (2.5
bar) developing in the boiler.
Route water hoses as short as possible and make sure they are
free of kinks. You must secure all hose connections in such a
way that they can withstand the system pressure and are water-
tight; this also applies to cold water hoses. Thermal expansion of
the water can cause pressures of up to 58 psi (4 bar) before the
over-pressure valve responds.
Webasto recommend that all water hoses be mounted at a
downhill slope to the heater wherever possible. You must route
intake and outlet pipes that are connected to the heater in such
a way that there are no drain traps. By doing so, if you drain the
boiler, you will also drain the water lines.
If you install the Dual Top ST heater outside, the water lines
must be routed within the air intake hose. This will avoid frozen
water lines as long as the heater is operating in the correspond-
ing mode. Also refer to the relevant Operating Instructions.
The Dual Top ST rubber bellow must be used to connect the air
intake hose to the heater. This must be secured with a clamp.
See Fig. 18.
NOTE
Do not fasten the rubber bellow with screws which ex-
tend into the rubber bellow and into the housing cover
with inlet interfaces because this may block the fans.

Hot water system | 8
9026389C II Dual Top ST 6 11 / 32
D
C
B
A
Fig.18
A Cold water line
B Hot water line
C Air intake hose
D Dual Top ST rubber bellow
8.1 Installation information for
submersible pump systems
The Dual Top ST application with a submersible pump system
requires a Dual Top ST heater with submersible pump version
and two extra ventilation hoses:
none ventilation hose for the cold water line, so that no wa-
ter is drawn from the vehicle’s fresh water tank while drain-
ing the boiler.
none ventilation hose for the Dual Top ST heater.
Fig.19 Dual Top ST application with submersible pump system
Number Description
1 Ventilation hose
2 Cold water line
3 Check valve
4 Ventilation hose Dual Top ST
5 Dual Top ST heater submersible pump version
6 Submersible pump
7 Vehicle’s fresh drinking water tank
8 Check valve
The numbers in Fig. 20 correspond with the same numbers in
Fig. 19.
1. Connect the ventilation hose (1) to the cold water line (2)
and mount the hose at a steep upward slope toward the
check valve (8).
2. Position the hose (1) in such a way that excess water flows
unimpaired from the vehicle to the ground.
CAUTION
uThe connection for the ventilation hose (1) and the
check valve (8) must lie above the vehicle fresh
drinking water tank (7).
uNo drain traps!
1. Connect the ventilation hose (4) to the hose which runs
through the housing cover with inlet interfaces (11) of the
Dual Top ST (5), and mount the hose with a steep upward
slope toward the check valve (3).
2. Position the hose (4) in such a way that excess water flows
unimpaired from the vehicle to the ground.
CAUTION
uThe ventilation hose (4) and the check valve (3) must
lie above the vehicle fresh drinking water tank (7)!
uNo drain traps!
uOutside the passenger compartment you must insu-
late the ventilation hose (4) to avoid frost!
Fig.20
Number Description
2 Cold water line
4 Ventilation hose Dual Top ST
5 Dual Top ST submersible pump version
9 Drain hose of overpressure valve and electrical
safety / drainage valve
10 Hot water line
11 Housing cover with inlet interfaces (service cap)
CAUTION
Never try to open the heater if you are not certified. In-
stallation and repair may only be carried out by persons
trained and certified in a Webasto training course.

9 | Hot air system
12 / 32 9026389C II Dual Top ST 6
9 Hot air system
NOTE
The heater must not be integrated into the vehicle heat-
ing system.
The recirculating air system ensures frost protection of the wa-
ter hoses with underfloor installation. It also contributes to a
high total efficiency and avoids fumes from the outside being
drawn inside. You can only use the recirculating air system
with air intake from the interior.
Use the control panel to adjust the interior temperature 41 to
95 ºF (5 to 35 ºC). Heat is generated with a diesel-operated
burner. The
Dual Top ST 8 also generates heat with an electric heater,
combining both devices (not available in North America). Power
of the Dual Top ST 8 electric heater, depending on the type and
setting:
nLow power = 1,000 W.
nHigh power = 2,000 W.
The heating capacity is automatically adjusted by the diesel
powered heater and modulated between 1,500 W and 6,000 W
depending on the output requirement. This is calculated from
difference between selected temperature and current interior
temperature.
To make sure that the heater functions satisfactorily, the flow
resistance of the connected hot air system must be minimized.
At maximum speed of the hot air fan, the maximum pressure
drop between the inlet and outlet side of the hot air line is 3.0
hPa (hectopascal).
Make sure that the air flow (air velocity) does not differ more
than factor two, comparing the two hot air distribution chan-
nels.
If the resistance of the hot air ducts is too high, the temperature
sensors inside the heater will detect a high air temperature. This
results in a higher speed of the hot air fan, causing more noise
and power consumption.
You must secure the hot air hoses (inlet and outlet) with clamps
or screws at their connection points.
NOTE
Check the installation for:
uNo air due to a short circuit between the vehicle‘s
heating system and the heater air inlet.
uNo air due to a short circuit between the heater‘s air
inlet and its air outlet, see also Fig. 21.
uNo air due to leakage from openings created to
route the hoses in or out of the interior.
1
2
12
Dual Top ST Dual Top ST
Fig.21
1 Air inlet for the heater
2 Air outlet for the heater
9.1 Heating air intake
9.1.1 General
NOTE
The heating air must be drawn from the interior.
Extracting heating air from an enclosure, such as the bottom of
the bed or the seat box, will reduce noise from the hot air fan.
Mounting the air intake in a central area provides even air circu-
lation throughout the interior.
Do not position the heating air inlet too low. This minimizes the
risk of dirt and small particles being sucked in. If necessary,
mount an air grille on the heating air intake.
Webasto recommend to position the inlet sufficiently above
floor level.
Make sure that no fluids can be spilled into the air inlet.
Fig. 22
If an air intake hose is used, its internal diameter must be
3.6 in (90 mm).
9.1.2 Installation
The length of air intake hose outside the interior shall be as
short as possible, ideally less than 3.3 ft (1 m). This is to
avoid heat losses and to protect the water pipes from
freezing. For the same reason, thermal insulation of the air
intake hose is re-quired.
Fig.23 Heating air intake
1. Determine the position of the hole in the floor through
which you want to pass the air intake hose.
2. Drill a hole in the floor with a diameter of 4 in (100 mm).
3. Seal the joint between the floor and the air intake hose
with temperature resistant sealing compound (up to 194 ºF
90 °C).
4. Outside the vehicle, insulate the air intake hoses to protect
the water lines against frost and to minimize energy loss.

Cooling air system | 10
9026389C II Dual Top ST 6 13 / 32
5. Inside the vehicle, guide the water pipes through the air in-
take hose.
6. Secure the air intake hose to the wall or the floor.
9.2 Hot air distribution
Design an air distribution system that provides an even distribu-
tion of heat into all heated sections of the vehicle. Design the
system so that the air flow through both heater outlets is sim-
ilar.
See the Webasto air and water heaters accessory cata-
logue or the Webasto motorhome product catalogue
for branches, connecting pieces, Y-junctions, outlets,
etc. made of high-temperature resistant materials.
The air distribution must be designed to be as uniform as pos-
sible to prevent possible air circulation in the hot air ducts in hot
water mode.
The housing cover with hot air outlet (see Fig. 2) is equipped
with two hot air outlets to which you must connect the hot air
hoses.
You must use both hot air outlets
The internal diameter of the main section of the two hot air
ducts must be 176 in (80 mm).
Guide the hot air with 176 in (80 mm) hoses directly from the
heater into the interior.
1. Connect 76 in (80 mm) hoses to the housing cover with hot
air outlet and secure them with screws to prevent them
from becoming detached during temperature changes (see
Fig. 2 and Fig. 24).
2. Connect the whole air distribution system using air distrib-
utors and reducers. Drill holes through the furniture and
floor where necessary. You can adjust the air flow, and
therefore the heat flow, through the selection of appropri-
ate branches and diameters.
3. Seal the gap between floor and hot air hose if the hot air
hose is going from the exterior to the interior of the vehicle.
4. Mount the Webasto air outlets at the end of each hot air
hose.
5. Insulate hot air ducts routed to the outside to minimize
energy loss.
6. In case hot air hoses inside the interior are not running
through closed compartments or areas, cover these hot air
hoses to prevent hose damage and accidental touching.
7. Secure the hot air hoses at all connection points using hose
clamps.
8. Secure the hot air hoses to the wall or floor using hose
clips.
NOTE
uMake sure that the length of the hot air ducts from
the heater to the first air outlet (from each heater
outlet) is at least 2.6 ft (0.80 m).
uYou must mount at least two air outlets (one each
per main section of the two hot air ducts) at the
same height. If possible, the air outlets with the
shortest hot air duct to the heater should be used.
uYou must ensure that the length of the hot air ducts
routed outside the passenger compartment is as
short as possible and insulated to keep heat loss to
a minimum.
uInstall hot air hose routing as straight as possible,
using large curves if necessary;
uAvoid compressing or pinching the hot air hoses.
uYou must not be able to close more than 30% of
the total number of outlets.
uPosition outlets in such a way that they are least
likely to get blocked. Free flow into the interior en-
ables the best interior heating and air circulation.
uPosition the outlets close to the floor / ground for
best air circulation.
CAUTION
Fire danger!
Only use high-temperature resistant Webasto hot air
hoses.
You must position the hot air opening in such a way
that air is not blown onto any parts that cannot with-
stand the heat. Depending on the length of the hot air
ducts, the blow-out temperature can be 248 ºF (120
°C) and briefly higher.
Fig.24 Hot air distribution
nDark grey: Below interior, insulated
nLight grey: Interior
10 Cooling air system
Cooling air is needed to protect the heaters’ electronics and the
motor against overheating. Cooling air must be taken from out-
side and not from inside the vehicle.
The air used has to be discharged outside the vehicle.
The heater is equipped with a motor and a fan to transport the
cooling air. Besides this, the fan also provides the heater with
combustion air.
This motor works independently from the hot air system that
has an own motor and fan.
10.1 Installation
Mount a grille on the cooling air inlet of the heater.
Also mount a cooling air inlet cover to prevent soiling and sub-
sequent blockage of the fan.
NOTE
A narrow cooling air inlet may lead to acceleration of
the fan and unnecessary noise.
Webasto therefore advise to keep the air intake resist-
ance to a minimum.

11 | Boiler drainage and pressure relief system
14 / 32 9026389C II Dual Top ST 6
1
2
Fig.25
1 Cooling-air inlet cover and protective grille, 60 mm dia-
meter
2 Protective grille only, 100 mm diameter
11 Boiler drainage and
pressure relief system
The heater is equipped with:
n
n
a drainage system that drains the water contents automat-
ically as a protection against frost (boiler water temperature
below 43 ºF, 6 ºC) or battery voltage has dropped below
10 volts for 30 minutes. It is also possible to drain the
system manually; a pressure relief system that prevents
pressure above 51 psi (3.5 bar) inside the boiler.
In both cases, water is drained off via a hose outlet exiting at
the bottom of the heater. The water is discharged under the
vehicle.
The drain hose of the overpressure valve and the electrical
safety / drainage valve (No. 9, Fig. 2) must be positioned and
routed so that the water flows unimpaired out of the vehicle
and onto the ground.
To completely drain the entire water system and the boiler,
Webasto advise using clean compressed air according to ISO
8573-1:2010, “Compressed air - Part 1: Contaminants and pur-
ity classes”. To do so:
1. Open all valves.
2. Connect compressed air with a pressure of approximately 2
bar to the hot water tap.
3. Leave the connection in place until no more water exits.
12 Fuel supply
12.1 General
The fuel is typically taken from the vehicle’s own fuel tank. It
can also be taken from a separate fuel tank (accessory). Suitable
fuel pumps are the DP 40 and the DP 42.4. The permissible val-
ues for the maximum pressure at the fuel pump entry side are
shown in Fig. 26 for DP 40 and Fig. 27 for DP 42.4.
NOTE
A notice, indicating that the heater must be shut down
before refueling, must be affixed to the fueling point. A
relevant sticker is part of the delivery scope.
Pressure table fuel supply for DP 40
Internal diameter (iø) = 2 mm
Length suction side (l1) ≤ 4.6 ft (1.4 m)
Length pressure side, (l2) ≤ 19.7 ft (6 m)
Permissible fuel supply-
line height H ft (m)
at max. pressure psi (bar) in
the fuel line
0.0 14.5 (1)
3.3 (1.0) 13.2 (0.91)
6.6 (2.0) 12 (0.83)
Maximum fuel supply-line
height S ft (m)
at max. negative pressure
psi (bar) in the fuel tank
0.0 -1.5 (-0.10)
1.6 (0.5) -0.09 (-0.06)
Fig.26 Permissible pressure at the fuel take-off point DP 40
Pressure table fuel supply for DP 42.4
Requirements for the fuel lines Value
Inside diameter 2mm
L1 Max length (intake side) ft (m) 16.4 (5 m)
L2 Max length (pressure side) ft (m) 33 (10 m)
L1 +
L2
Max overall length ft (m) 39.4 (12 m)
H1 Max height difference form heater-
fuel pump (heater above fuel pump)
29.4 (3 m)
H2 Max height difference form heater –
fuel pump (heater below fuel pump)
3.3 (1 m)
h1 ft (m)pmax psi (bar)
h1 = 0 -1.5 to +7.25 (-0.1 to +0.5)
h1 = 0 to 3.3 (0 to 1) -1.5 to +5.8 (-0.1 to +0.4)
h1 = 3.3 to 6.6 (1 to 2) -1.5 to +4.4 (-0.1 to +0.3)
h2 ft (m) pmax psi (bar)
h2 = 0 to 4.3 (0 to 1.3)-1.5 to +7.25 (-0.1 to +0.5)
Fig.27 Permissible pressure at the fuel take-off point DP 42.4
12.2 Fuel pump
The fuel pump DP40 and the fuel pump DP42.4 provide a com-
bined delivery, metering and a shut-off system. The pumps are
subject to certain installation criteria (see Fig. 26 and Fig. 27).

Fuel supply | 12
9026389C II Dual Top ST 6 15 / 32
12.2.1 Installation location
You must not install the fuel pump and its fuel lines within
range of hot vehicle parts which radiate heat. Use a heat shield
if necessary.
The fuel pump must be mounted outside the vehicle.
A
Fig.28 Mounting location (A) for fuel pump on heater
Mounting the fuel pump on the heater (see Fig. 28, "Mounting
location (A) for fuel pump on heater") is only allowed if the
length of the fuel line’s suction side does not exceed 4.6 ft (1.4
m).
If the length of the fuel line’s suction side is over 4.6 ft (1.4 m),
then the fuel pump and the heater have to be installed separate
from each other. In this case you must extend the fuel pump’s
wiring harness.
NOTE
You can reduce the vibration level by mounting the fuel
pump on the sturdiest possible part of the vehicle
chassis, such as a frame side member. As a result, the
ticking noise of the fuel pump may be perceived as be-
ing more quiet.
12.2.2 Installation and attachment
The fuel pump installation position is limited as shown in Fig. 29
to ensure effective automatic bleeding.
The fuel pump must be installed in a horizontal position (0 to
5º).
To reduce noise, the fuel pump must be installed with a vibra-
tion-damping suspension.
Pay attention to the direction of the fuel flow. The arrow on the
fuel pump must point towards the heater.
0 - 5°
Fig.29 Fuel pump DP40 installation position
The next picture shows the installation position for the fuel
pump DP 42.4
+90°
-45°
0-360°
WHE000016A
Fig.30
12.3 Fuel extraction
For recommended fuel extraction solutions see Webasto mo-
torhome product catalogue.
Installation into the vehicle’s fuel line:
a) T-junction from the fuel line to the vehicle’s engine if no de-
livery pump is installed inside the tank.
b) T-junction from the fuel return line to the tank, if a delivery
pump is installed in the tank. Make sure that the fuel return
line inside the tank goes nearly to the bottom of the tank,
otherwise the heater will receive no fuel if the tank’s fuel
level is low.
NOTE
Webasto recommend that the fuel be pumped out of
the return line. Please confirm before installation
whether this is possible for your vehicle type.
Contact a Webasto Service Centre.
NOTE
Both options are only feasible if the fuel pressure at the
connection point to the fuel line does not exceed the
specified values in chapter12.1, "General" on page 14.
The line from the T-junction towards the fuel pump
should run downwards.
nThe fuel can be taken from the vehicle’s own fuel tank or
from a separate tank with a fuel extractor. See Fig. 32.
nThe fuel standpipe must be mounted in the fuel-tank
sender unit. The fuel-tank sender unit must be removed
previously. When drilling the hole, make sure to use a plain
and even surface for correct sealing.
nWebasto fuel extractor, see Fig. 33.
Observe the installation instructions for the different fuel ex-
tractor types.
Fig.31 Connection to vehicle's fuel line using a Webasto fuel connector

13 | Combustion air supply
16 / 32 9026389C II Dual Top ST 6
1
2
3
Fig.32 Webasto fuel extractor
1 Fuel standpipe
2 Sealing ring
3 Fuel-tank sender unit
1
≥25 mm
Fig.33 Webasto fuel extractor (side view)
1 Hole pattern
12.4 Fuel lines
In accordance with DIN 73378, only steel and plastic lines of
plasticized, light and temperature-stabilized PA 11 or PA 12,
such as Mecanyl RWTL, may be used as fuel lines. Because the
lines cannot normally be routed with a constant rising gradient,
the internal diameter must not exceed 2 mm. In larger fuel lines
air or gas bubbles would accumulate and cause malfunctions.
12.4.1 Routing
The lines should be routed upwards from the fuel pump to the
heater to facilitate automatic bleeding.
Avoid passing or crossing of hot areas, such as the exhaust line,
at a distance of less than 3.9 in (100 mm) without using
thermal shields.
Fuel lines must be secured to the vehicle’s chassis to prevent
sagging. They must be installed in such a way that they cannot
be damaged by flying road chippings or high temperatures (ex-
haust line). The fuel lines must be secured at the connections
using hose clips to prevent them from detaching.
12.4.2 Connecting two pipes with a hose
The correct procedure for connecting fuel lines with hosing is
shown in Fig. 34.
Make sure that there are no leaks.
C1
2
2
W
Fig.34
C Correct
W Wrong
1 Clip
2 Air or gas bubble
12.5 Fuel filter
You must not use a fuel filter in the heater fuel system. This is
due to the possibility of frost affecting the moisture contained
in the air bubbles, the fuel supply could be completely blocked
in case of frost.
13 Combustion air supply
13.1 General
The air for the combustion chamber of the heater must not be
taken from the vehicle’s passenger compartment (excerpt from
ECE-R 122).
Maximal total length of the combustion air inlet
pipe (including silencer)
2.0 m
Internal diameter of the pipe - in (mm) 0.9 (22)
Minimal bending radius - in (mm) 2 (50)
Maximal total bends of the combustion air pipe in
degrees
270°
NOTE
An air intake silencer must be fitted to reduce the noise
level.
The combustion air must be taken from an area that is
protected from splashing water and as cool as possible.

Exhaust system | 14
9026389C II Dual Top ST 6 17 / 32
13.2 Combustion air intake line
A Connection to heater 22 mm diameter
B Silencer
An intake pipe is required for combustion air.
NOTE
uAvoid the air intake pipe being compressed or
pinched.
uThe intake opening for combustion air must be loc-
ated so that it cannot become clogged with dirt or
snow. See Fig. 36.
A
B
Fig.35 Combustion air intake
Fig.36 Avoid the intake pipe becoming clogged
NOTE
The intake opening for combustion air must not point
in the driving direction. See Fig. 37.
Dual Top ST Dual Top ST
Fig.37 The end of the pipe must not point towards the front of the
vehicle
Combustion air intake hose must point downwards from the
heater. If this is impossible, you must drill a condensate drain
hole with a diameter of 5/32 in (4 mm) at the lowest point of
the pipe.
See Fig. 38.
Dual Top ST Dual Top ST
Fig.38 Prevent condensation forming
14 Exhaust system
14.1 General
See chapter3, "Statutory Regulations governing installation" on
page 3 for requirements on exhaust system.
NOTE
uAn exhaust silencer must be fitted to reduce the
noise level.
uThe silencer should ideally be installed near the
heater (not more than 7.9 in, 0.20 m distance);
followed by a long tail pipe (min. 3.3 ft, 1 m) for
best noise level reduc-tion.
uThe silencer may be mounted on the vehicle chassis.
It may also be mounted on the heater (see Fig. 39).
Fig.39 Exhaust silencer mounted on a heater
Fig.40 Exhaust silencer (arbitrary flow direction)
14.2 Exhaust line
Exhaust lines use flexible piping of stainless steel or rigid pipes
of stainless steel with a minimum wall thickness of 0.4 in (1.0
mm). The exhaust pipe has to be connected to the heater using
a Webasto exhaust clamp. You can use an exhaust assembly in-
cluding a special bracket to mount the silencer on the heater.

14 | Exhaust system
18 / 32 9026389C II Dual Top ST 6
Max total exhaust pipe length (including si-
lencer) - ft (m)
9.9 (3.0)
Internal diameter of the stainless steel pipe -
in (mm)
0.9 (22)
Minimal bending radius (mm) 2 (50)
Maximal total exhaust line bend in degrees 270°
nOnly one piece of cast 90° elbow is allowed.
nPipes with 90° bends or more are allowed. See Fig. 41.
nThe exhaust line must point from the heater downwards to
allow condensation water to drain (see Fig. 38). If this is
not possible, you must drill a condensation drain hole with
a diameter of 5/32 in (4 mm) at its lowest point.
nThe exhaust line must not point to the front of the vehicle.
See Fig. 44.
nAvoid the formation of an exhaust accumulation under the
vehicle. See Fig. 44.
nDischarge direction: 45° to 70°.
A fixing bracket is required no further than 6 in (150 mm)
from the end of the exhaust pipe to ensure that the angle 45°
to 70° is achieved.
CAUTION
If the exhaust pipe end is other than as shown, it will
pose a fire risk. See Fig. 44.
uThe complete exhaust system must be located out-
side the vehicle.
uAssemble the line in such a way that it cannot set
fire to anything.
u
u
The pipe must be located so that it cannot become
clogged with dirt or snow. See Fig. 36.
The pipe must be installed at a minimum distance of
12 in (300 mm) from windows, ventilation openings,
gas bottles and gas-bottle storage rooms. See also:
NEN 1949, "Specification for installation of LPG
systems".
CAUTION
uThe pipe must be routed so that a minimum dis-
tance of 19.7 (500 mm) to the fuel system is
maintained.
uThe exhaust gas outlet must not be located directly
under a door, a window or any other ventilation
opening. Make sure that the exhaust gas is not
blown toward a neighbouring tent or motorhome.
uThe exhaust outlet must be on the opposite side of
the entrance door of the living cell.
uMake sure there is sufficient ground clearance, so
the exhaust system cannot touch the ground or
pavement, taking any traffic calming measures into
account.
Fig.41 Elbows: cast pipe (left) and bent pipe (right)
Dual Top ST Dual Top ST
Fig.42 Prevent condensation forming
Fig.43 Avoid the exhaust pipe becoming clogged
A
B
C
Fig.44 Location and direction of the exhaust
A Direct the flow of exhaust fumes 45° to 70° downwards
on the side of the vehicle to avoid accumulation of fumes
under the vehicle.
B Make sure that the end of the exhaust is almost aligned
with the side of the vehicle body.
C Make sure that the end of the exhaust is cut horizontally
to avoid ambient wind entering.

Electrical connections | 15
9026389C II Dual Top ST 6 19 / 32
15 Electrical connections
15.1 Schematic connection diagrams
Carry out electrical connections in accordance with Fig. 45 or Fig. 46.
NOTE
When installing the Dual Top ST wiring harness in the vehicle, you must make sure that no wires can become strained.
Fig.45 Schematic diagram of electrical connections Dual Top ST 6
Nu
m-
ber
Description
1 Dual Top ST 6
2 Wiring harness
3 Manual or programmable control panel
4 Vehicle‘s service battery
5 Fuse 5 A
6 Fuse 15 A
7 Fuse 15 A
8 Fuel pump
9 Interior temperature sensor
10 Wiring interior temperature sensor
Fig.46 Schematic diagram of electrical connections for Dual Top ST 8
Nu
m-
ber
Description
1Dual Top ST 8
Not Available In North America
2 Wiring harness (external)
3 Programmable control panel
4 Vehicle’s service battery
5 Fuse 5 A
6 Fuse 15 A
7 Fuse 15 A
8 Fuel pump
9 Interior temperature sensor
10 Wiring interior sensor
11 Receiver Telestart
12 Relay box
13 Wiring harness of the electric heater (integ-
rated)
14 Wiring 230 V
15 230 V power supply

15 | Electrical connections
20 / 32 9026389C II Dual Top ST 6
15.2 Supply voltage connection
Use 12 V DC only
Make sure you take power directly from the vehicle‘s service
battery. You must not use any additional switches with the ex-
ception of the control panel switch.
You must switch the heater on and off with the Dual Top ST
control panel.
The fuse holder must be installed in the interior of the vehicle.
Use fuses:
n5 A
n15 A
n15 A
Fuses must be connected to the correct wires in each case (ob-
serve the colour codes).
n5 A: red-and-blue cable
n15 A: red-and-black cable
n15 A: red cable
After connecting the cables, make sure that the yellow part is
pushed into each fuse holder correctly. This prevents cables be-
ing pushed out when inserting or replacing a fuse. See Fig. 46.
NOTE
Make sure that the Dual Top ST heater is switched off
before you replace a fuse.
CAUTION
In case of electrical deviations, using fuses other than
the specified ones may cause a fire.
Fig.47
Fig.48 Fuse holder, installation and position
15.3 Interior temperature sensor
The remote interior temperature sensor must be installed at me-
dium height in the interior on vertical surfaces.
Make sure that the inside temperature sensor is not positioned:
nin the direct current of hot air (from the vehicle heating sys-
tem or from the Dual Top ST heater).
nclose to heat sources.
nplaced in direct sunlight (for example on the dashboard).
ninstalled inside a locker.
ninstalled behind curtains or similar.
Make sure that cabin air can flow freely around the sensor.
To install the remote interior temperature sensor in the interior:
1. Drill a 3/8 in (10 mm) hole just below the position of
the sensor.
2. Remove the blade connector from the cable to enable it to
be guided through easily.
3. Lead the sensor cable through the hole.
4. Secure the sensor.
5. Route the cable to the location of the control panel.
6. Remount the blade connector on the sensor cable.
7. Secure the wires to the wall or to the floor.
Fig.49
15.4 Connection to manual control
panel
Positioning and installing the manual control panel
1. The control panel must be located in the driver's field of
view.
2. The control panel should be visible and accessible to the
operator. It must not be accessible to children however.
3. –15° < best viewing angle < +15°.
4. Make sure that there is enough space behind the location
where the control panel will be mounted.
5. Cut the aperture in the desired installation location (see Fig.
50).
6. Connect the X4 plug (4 poles) of the wiring harness to the
control panel (see Fig. 51).
7. Connect the X0 plug (2 poles) of the inside temperature
sensor to the control panel (see Fig. 51).
8. Mount the control panel using the 4 screws.
9. Click the cover onto the control panel.