MHS Boilers Strata 2 User guide

GAS FIRED HIGH EFFICIENCY/
CONSDENSING ULTRA LOW NOx BOILER
SINGLE UNIT OUTPUT 120kW
INSTRUCTIONS FOR INSTALLATION,
SERVICING & OPERATION
STRATA2

2
STRATA2
Index
page section
3
. . . . . . . . . 1.0 General
1.1 Product Description
1.2 Certification Details
3-5 . . . . . . 2.0 Product Description
6 . . . . . . . . . 3.0 Technical Details
3.1 Technical Data
7 . . . . . . . . . 3.2 Critical Dimensions
8 . . . . . . . . . 3.3 System Guidance
3.4 Flue Options
4.0 Appliance Installation
Requirements
4.1 Statutory Requirements
8-9 . . . . . . 4.2 Boiler Position
9-15 . . . . 4.3 Flue Options &
Terminal Position
15 . . . . . . . 4.4 Ventilation
Requirements
16-17 . . 4.5 Hydraulic System
Design
17 . . . . . . . 4.6 Gas Supply
4.7 Electrical Supply
18 . . . . . . . 5.0 Installation Instructions
5.1 Unpacking the Boiler
5.2 Positioning the Boiler
5.3 Air Supply &
Exhaust Connections
5.4 Gas Connection
19 . . . . . . . 5.5 Water Connections
5.6 Condense Waste
Connections
5.7 Electrical Connections -
General
5.7.1 Connecting the
Power Supply
20 . . . . . . . 5.7.2 Connecting of System
Safety Interlocks
20-23 . . 5.7.3 Connecting of System
Safety Interlocks
Connection Diagrams
24 . . . . . . . 5.7.4 Electrical
Wiring Diagrams
25 . . . . . . . 5.7.5 Connecting Remote
Fault Alarms
5.8 Connecting Additional
Boilers
5.8.1 Connecting Third,
Fourth, Fifth,
Sixth, Seventh and
Eighth Units
page section
25
. . . . . . . 5.8.2 Boiler Manager RVA 47
Installation Procedure
(Normally Factory
Fitted)
26 . . . . . . . 5.8.3 Mixing Valve Controller
RVA 46 Installation
Procedure
5.9 Connecting a
Condensate Pump
27 . . . . . . . 5.9.1 Condensate Receptacle
and Pump -
Model No. KHPI
6.0 Commissioning
and Testing
6.1 Filling the Boiler
28 . . . . . . . 6.2 Appliance Operation
Left Switch Panel
6.2.1 Left Switch Panel
6.2.2 Module Control Panels
29 . . . . . . . 6.2.3 DIP Switches
30 . . . . . . . 6.3 Firing the Appliance
6.3.1 Initial Start Up
6.4 Setting and Adjusting
the Load
31 . . . . . . . 6.4.1 Setting Minimum Load
6.4.2 Setting Maximum Load
6.4.3 Setting Maximum/
Minimum Load for
Upper Module
6.5 Setting for Propane Gas
32 . . . . . . . 6.6 Setting Domestic
Hot Water
6.7 Switching Off
the Appliance
7.0 Boiler Control Settings
32-33 . . 7.1 End User
Parameter Settings
33-36 . . 7.2 Heating Engineer
Parameter Setting
37-38 . . 7.3 OEM Parameter Setting
38 . . . . . . . 8.0 Maintenance and
Inspection
8.1 Inspection
39 . . . . . . . 8.2 Maintenance
9.0 Fault Diagnosis
9.1 Control Panel
39-40 . . 9.1.1 Operation Indicator
9.1.2 Fault Indicator
41 . . . . . . . 9.1.3 System Faults
9.2 RVA 47 Fault Indication
42 . . . . . . . 10.0 Parts List
11.0 Guarantees

3
1.0 general
STRATA2
1.1 general notes
These instructions are intended to assist the installer, commissioning engineer, maintenance engineer
and user with the installation, maintenance and usage of the Strata 2-120 gas fired condensing boiler.
Please read this manual fully before commencing the installation of the appliance. MHS Boilers Ltd shall
not be responsible for any damage resulting from failure to carefully observe the instructions given.
The Strata 2-120 must only be installed by persons deemed to be competent i.e. Corgi Registered. This
manual must be handed to the user following completion of the installation.
1.2 certification details
The Strata 120-2 complies with all relevant European Directives and has been independently certified
to comply with the requirements of prEN 483 for use in GB and IE with Gas Category II2H3P.
(Natural gas G20 @ 20 mbar inlet pressure).
The flue classification (depending upon the required flue option) is either B23; C13X; C33X; C43X;
C53X; C63X; C83X.
CE
0063AT3426-98
2.0 product
description
The Strata 2-120 boiler is a gas-fired, fully condensing floor standing appliance with a fully modulating
output of 12.2 to 119.7 kW at 30ºC return water temperature. The appliance may be used singularly or in
multiples serving the needs of LTHW systems up to a maximum flow temperature of 85ºC.
Each Strata 2-120 boiler incorporates two modules, each module accommodates its own burner,
combustion fan, gas valve, ignition/ionisation, electrode and burner control with safety circuits.
Each module contributes 50% of the total output, and can be operated independently. Each heat
exchanger has a modulating capacity of 20% to 100%. If a fault should occur with one of the burner/heat
exchanger modules, the other will continue to operate.
The boiler includes, as standard, matched modulating speed pumps which automatically adjust the
primary flow rate for the heat exchangers to (where possible) maintain the design temperature difference.
The pumps have residual duty to convey the boiler mass flow rate to the installers system low loss manifold,
ensuring correct flow rates through the boiler at all times and reduces installer involvement in this
critical area.
The Strata 2-120 incorporates comprehensive microprocessor controls. A RVA47 (CLI) cascade
manager is used to translate the heat demand of the installation into a boiler load for each module. The
first RVA47 (CLI) manager has the potential to control up to four modules (burner/heat exchangers) in
modulating/cascading fashion. Therefore when installing Strata 2-120 boiler in twin form, all serving the
same system, an RVA47 (CLI) controller is only required and supplied in the first boiler.
The RVA47 (CLI) controller in boiler no.1 is always the ‘master’ and every subsequent controller must
be set as a ‘slave’.
In addition to the RVA47 (CLI) controller, each Strata 2-120 boiler incorporates individual burner/heat
exchanger safety controls which provide the essential safety functions of burner ignition and flame
monitoring, overheat cut off devices for excessive water or flue gas temperature, an LCD display screen
to indicate run or fault status codes, and individual burner on/off switches.
Room Sealed Option
When required, the Strata 2-120 boiler, may be installed as a room sealed appliance, taking air for
combustion from outside the building. This option is recommended for installations where air from within
the building may be contaminated with oxidising agents, which occur in appliances such as swimming pool
plant rooms, dry cleaners and in various manufacturing and industrial process environments etc.

4
STRATA2
2.0 product description (contd)
Extended Flue Lengths and Difficult Flue Routes
The excess fan pressure from the combustion system is in the order of 100Pa which allows the
appliance to be exhausted using small diameter flue components over long distances or awkward routes,
which allows a considerable degree of flexibility in boiler siting.
As the efficiency of this unit is extremely high, high grade plastic flue components can be utilised
because the temperature of the flue gas will at all times remain below 80ºC. (To protect the plastic
discharge pipe against excessive temperatures, a safety thermostat is employed set at 80ºC, which is fitted
inside the plastic discharge pipe in the unit, immediately above the upper heat exchanger).
Note: These flue components are available exclusively from MHS.
The Strata 2-120 includes a wealth of enhanced operating facilities and features as standard:
●Floor mounted with compact dimensions (provides maximum heat from a minimal
footprint).
●Fully modulating heat output: The output is fully variable across the twin burner/heat
exchanger arrangement providing a 10:1 turn down ratio, sliding between 10% and 100% of output
which automatically and instantly adjusts to meet the needs of the system. The percentage of power
at any given time may be dictated by flow temperature, outside air temperature, room temperature,
stored domestic hot water temperature or a combination of these.
●Fully condensing stainless steel heat exchanger. The Strata 2-120 boiler features a heat
exchanger which deliver exceptional heat transfer, and is fabricated from corrosion resistant, long life,
stainless steel. The uniquely designed Spiranox heat exchanger will return operating efficiencies of up
to 105% nett (95.5% gross) with a return water temperature of 30ºC.
●Extremely low harmful emissions. The boiler utilises 100% premixed gas/air fed at positive
pressure to the metal fibre sheathed radiant burners. The optimum amount of gas/air is mixed before
the combustion fan, and then blown into the burner.
●Single/double heat exchanger operation for maximum flexibility of operation.
A spring loaded non-return valve has been fitted in the air intake to the combustion fan, preventing flue
gases from a firing module from entering the air intake of the non firing module. Also a hydraulic non-
return valve is fitted in each heat exchanger return pipe to prevent circulation of water if one of the
heat exchangers is not functioning.
●Low CO and NOx emissions. The advanced burner and controls allows extremely clean and
efficient combustion to be achieved, which in turn gives extremely low emissions certified in
accordance with DIN 4702, CO 15mg/kWh (14ppm) –Nox 11mg/kWh (8.0ppm).
●Accurate variable burner output control. The premix fans have very accurate speed control
which allows precise control over combustion air volumes. This system facilitates great accuracy and
instantly provides variable burner output. The nature of the variable rate fans allows, in the case of a
lower heat demand, the fan to run at a slower speed, resulting in lower power consumption.
●Each boiler incorporates LCD display screens to display current operational status and
operational parameters. Each RVA controller provides cascade modulating burner output control,
hours run counters for each burner and programmable lead/lag sequencing.

5
STRATA2
2.0 product description (contd)
●The ‘master’RVA47 (CLI) controller provides:
•Overall modulating output in accordance with the demands of the system.
•Inbuilt weather compensation giving direct-on-boiler VT control if required.
•Remote stored domestic hot water temperature control
•Domestic hot water primary pump or diverter valve control. (2 Amps max)
•Heating system pump control. (2 Amps max)
•Inbuilt heating system time control with 35 on and 35 off programmable set points within 7 days.
•Inbuilt DHW time control with 3 on and 3 off sets points per day.
•An option to control the boiler/s from external 0-10V input, or volt free switching.
•Programmable frost protection.
•The additional option to connect remote control devices.
•The additional option to connect VT zone controllers. (RVA46)
Designed for Ease of Maintenance
The appliance has been designed and engineered to be easy to maintain, with most major service
operations being quick and easy to complete with the minimum of tools.
Each module can operate independently, without affecting the service of the other modules within
the system.
To facilitate the annual inspection and cleaning of the syphon, there is a rinsing pipe at the back of the
unit. The condense is led through a built-in syphon to a plastic connection at the back, where a suitable
connection can be made to the termination point.
Operational Data Logging
Each burner assembly has a data logging facility to record operational actions, which can be accessed
via an RS232 communication from a PC. This facility provides a useful service tool as it allows a record of
operation to be viewed and any faults to be identified.

6
STRATA2
3.0 technical
details
3.1 technical data
Table 1
Model Strata 2
No. of Boilers
No. of Burners/
Ht Exchangers
No. of Cascade RVA Controllers
Master & Slaves
Output Turn Down Ratio
Max kW
Heat Output at Min
80°C Flow - 60°C Return Max Btu/h
Min x 1000
Max kW
Heat Output at Min
50°C Flow - 30°C Return Max Btu/h
Min x 1000
Nominal Heat Nett kW
Input Max Btu/h
Input Rate m3/h
NatGas Max ft3/h
Flow Temperature Max °C
Max Operating Pressure Bar
Min Operating Pressure Bar
Flue Gas Volume m3/h
Max Hot
Combustion m3/h
Air Volume Max
Flue Gas °C
Temperature Max
Gas Inlet Pressure mbar
(NatGas) Min/Max
Flow & Return BSP-M
Connections
Gas Connection BSP-M
Flue Connection mm
Air Tube Connection mm
(for room sealing)
Weight Empty kg
Full
Water Content L
Electrical Supply 1 Phase
Electrical Load Max Watts
Condense Waste BSP-M
Connection
Single
120
1
2
1 master
10:1
107.8
11.1
367
37
119.7
12.2
408
41
114
388,968
12.06
426
85
4.0
0.5
170
130
80
15/60
11/4"
1"
110
110
155
170
15
1 x 230V
260
3/4"
240
2
4
1 master
20:1
215.6
11.1
735
37
239.4
12.2
816
41
228
777,936
24.12
852
85
4.0
0.5
340
260
80
15/60
11/4" (x2)
1" (x2)
110 (x2)
110 (x2)
310
340
30
2 x 230V
2 x 260
3/4" (x2)
360
3
6
1 master
+ 1 Slave
30:1
323.4
11.1
1,103
37
359.1
12.2
1,225
41
342
1,166,904
36.18
1278
85
4.0
0.5
510
390
80
15/60
11/4" (x3)
1" (x3)
110 (x3)
110 (x3)
465
510
45
3 x 230V
3 x 260
3/4" (x3)
480
4
8
1 master
+ 2 Slave
40:1
431.2
11.1
1,471
37
478.8
12.2
1,633
41
456
1,555,872
48.24
1704
85
4.0
0.5
680
520
80
15/60
11/4" (x4)
1" (x4)
110 (x4)
110 (x4)
620
680
60
4 x 230V
4 x 260
3/4" (x4)
600
5
10
1 master
+ 3 Slave
50:1
539
11.1
1,839
37
598.5
12.2
2,042
41
570
1,944,840
60.3
2130
85
4.0
0.5
850
650
80
15/60
11/4" (x5)
1" (x5)
110 (x5)
110 (x5)
775
850
75
5 x 230V
5 x 260
3/4" (x5)
Multiple Boilers Multiple Boilers

STRATA2
7
600
150
725
97
108
58
A
C
B
D
222
162
50
690
410
279
35
66
36
FE
G
B
A
40
50
275
1570 1370
220
G
B
A
E
F
plan
rear
side
A Return (R11/4")
B Flow (R11/4")
C Flue Outlet 110 Dia
D Air Inlet 110 Dia
E Condense-Outlet
(R3/4")
F Syphon clean point
G Gas (R1")
Dimensions in millimetres
Note:
Re flow and return connections. Each boiler is
equipped with 2Nr flow and 2Nr return
connections. The installer may use either both
top or both rear or one of each.
Clearances mm
Front min 500 - recommended 750
Rear min 450
Top min 500
AB
Boiler to boiler - none
A - None when B = 450
B - None when A = 450
3.2 critical dimensions
appliance dimensions
installation clearances
Fig 3.2a
Fig 3.2b

8
STRATA2
3.3 system guidance
In summary, the Strata is designed for use with a sealed pressurised hydronic circuit operating upon a
design temperature difference of 20ºC. The integral primary pumps have approximately 1m head available
to overcome a primary loop incorporating a low velocity mixing header. Full details regarding suitable
system designs are given in section 4.3.
3.4 flue options
The Strata 2-120 may be used with either an open or room sealed flue and air system. Approximately
100Pa is available as residual flue pressure at the exit from the appliance. Full details regarding flue
specification are given in section 4.3.
4.0 appliance
installation requirements
4.1 statutory requirements
Gas Safety (Installation and Use) Regulations (Current Issue)
It is the law that all gas appliances are installed by a registered person, in accordance with the above
regulations. Failure to install appliances correctly could lead to prosecution. It is in your own interest, and
that of safety, to ensure that the law is complied with.
In addition to the above regulations, this appliance must be installed in accordance with the current IEE
Wiring Regulations for electrical installation, (BS 7671), Local Building Regulations, the Building Standards
(Scotland) (Consolidation) Regulations, Bye laws of the Local Water Undertaking and Health and Safety
Document No. 635 ‘The Electricity at Work Regulations 1989’.
It should also be in accordance with the relevant recommendations in the current editions of the
following British Standards and Codes of Practice, plus any others that are relevant to the proposed
installation: BS5449, BS5546, BS5440:1, BS6798, BS6891, BS6644, BS6880, IGE/UP/2, IGE/UP/7, & IM11.
Clean Air Act Memorandum on Chimney Heights.
Important Note: Manufacturer’s instructions must NOT be taken in any way as overriding
statutory obligations.
4.2 boiler position
The following considerations must be observed when siting the Strata 2-120:
The boiler is not suitable for external installation. The position selected for installation should be within
the building, unless otherwise protected by a suitable enclosure, and MUST allow adequate space for
installation, servicing, and operation of the appliance, and for air circulation around it. (Refer to figure 4.3e).
In a multiple set-up (modular set-up), the sides of the units may be placed against one another, without any
room in between.
This position MUST allow for a suitable flue system and terminal position (Refer to sections 4.3). A
connection to a suitable termination point for the discharge of condense must be available . If this is not
present, a condensation pump with an elevation level of 5 metres may be fitted to the appliance. The Strata
2-120 must be installed on a flat horizontal floor which is capable of supporting the boiler and any ancillaries
(circa 200kg).
If the appliance is to be fitted in a timber framed building it should be fitted in accordance with the
British Gas publication ‘Guide for Gas Installations In Timber Frame Housing’, Reference DM2. If in doubt,
advice must be sought from the Gas Supplier.
If the appliance is to be installed in a room containing a bath or a shower, any electrical switch or
control utilising mains electricity must be so situated that it cannot be touched by a person using the bath
or shower. Attention is drawn to the requirements of BS7671 (the current I.E.E. Wiring Regulations), and
in Scotland the electrical provisions of the Building Regulations applicable in Scotland.
A compartment used to enclose the appliance MUST be designed and constructed specifically for this
purpose. An existing cupboard, or compartment, may be used provided it is modified accordingly. BS
5376:2 gives details of the essential features of cupboard/compartment design, including airing cupboards.

9
4.2 boiler position (contd)
STRATA2
Where installation will be in an unusual location, special procedures may be necessary. BS6798 gives
detailed guidance on this aspect.
The unit cannot be used in the vicinity of chlorine, halogen or sulphur as may be the case in
environments such as swimming pools, coolant filling stations etc. In such cases the appliances MUST be
room sealed to take air for combustion from outside of the building.
●DN100 PPS tube x 1000mm
●DN100 PPS bend x 90°
●DN100 PPS bend x 45°
●DN100 wall bracket
●DN125 PPS tube x 1000mm
●DN125 PPS bend x 90°
●DN125 PPS bend x 45°
●DN125 wall bracket
●DN150 PPS tube x 1000mm
●DN150 PPS bend x 90°
●DN150 PPS bend x 45°
●DN150 PPS tee with 45°branch
●DN100 x 125 PPS increaser
●DN125 x 150 PPS increaser
●DN150 wall bracket
●100/100 to 100/150 concentric adaptor
●100/150 concentric tube x 1000mm
●100/150 concentric bend x 90°
●100/150 concentric bend x 45°
●100/150 concentric horizontal terminal effective
length 975mm
●100/150 concentric vertical terminal effective
length 500mm
●DN100 flat roof flashing
●DN100 pitched roof flashing
●DN125 flat roof flashing
●DN125 pitched roof flashing
●DN150 flat roof flashing
●DN150 pitched roof flashing
●Flat roof for 100/150 concentric terminal
●Adjustable pitched roof flashing for 100/150
concentric terminal
4.3 flue options &
terminal position
The Strata 2 has an excess pressure combustion system that allows the appliance to be exhausted over
extended distances using small OD flue components.
The flue gas temperature is extremely low (typically the same as the flow water temperature), which
allows the use of easy to install PPS (polypropylene) flue pipe and fittings.
The appliance can take combustion air from the room in which it is installed (conventional application)
or can be room sealed (fanned balanced flue) using a concentric flue arrangement of a 100mm PPS flue
duct within a 150mm galvanised metal air duct, finished in off-white RAL 7035. A full range of flue pipe and
air duct components including roof and wall terminals is available from MHS Boilers.
list of flue components
calculating flue resistance
The excess pressure available for overcoming the frictional resistance of a flue system is 100 P.a. The
table of flue component resistances will assist the designer in calculating total flue system frictional loss.
If the total installed flue system resistance exceeds 100 P.a., then the result will be a reduction in boiler
output. Reference to the “Effect of Flue System Resistance On Boiler Output”, graphs will assist. If the
resistance of a proposed flue system has an unacceptable effect on boiler output, then a larger diameter
flue tube should be selected. Thermal up-draught is generated in a vertical flue system, reducing the
resistance of the system. Reference to the “Thermal Up-draught Graph”will provide a figure in P.a., which
may be deducted from the total calculated flue system resistance.
Note: Does not apply to horizontal sections of a flue system.

10
STRATA2
4.3 flue options & terminal position (contd)
PPS Component Resistance Pa For Single Boiler
1m Length DN100 Flue Gas tube 7.0
1m Length DN100 Tube Carrying Air 4.0
90°Bend DN100 Carrying Flue Gas 7.0
90°Bend DN100 Carrying Air 4.0
45°Bend DN100 Carrying Flue Gas 4.0
45°Bend DN100 Carrying Air 2.0
1m Length 100/150 Concentric Tube 12.0
90°100/150 Concentric Bend 12.0
45°100/150 Concentric Bend 6.0
100/150 Concentric Terminal 15.0
Vertical or Horizontal
100/100 to 100/150 Concentric Adaptor 2.0
DN100 Open Termination with Bird Mesh 7.0
DN100 Air Tube Termination with Rain Cap 8.0
DN125 Air Tube Termination with Rain Cap 5.0
PPS Component Resistance Pa For Single Boiler
DN150 Air Tube Termination with Rain Cap 2.0
1m Length DN125 Flue Gas tube 2.5
1m Length DN125 Tube Carrying Air 1.5
90°Bend DN125 Carrying Flue Gas 2.5
90°Bend DN125 Carrying Air 1.5
45°Bend DN125 Carrying Flue Gas 1.5
45°Bend DN125 Carrying Air 1.0
DN125 Open Termination with Bird Mesh 2.5
DN150 Open Termination with Bird Mesh 1.0
1m Length DN150 Flue Gas tube 1.0
1m Length DN150 Tube Carrying Air 0.5
90°Bend DN150 Carrying Flue Gas 1.0
90°Bend DN150 Carrying Air 0.5
45°Bend DN150 Carrying Flue Gas 0.5
45°Bend DN150 Carrying Air 0.5
Table 3
examples of calculating flue pressure loss
140
130
120
110
100
90
80
70
60
50
40
30
20
10
0
0246810121416182022242628303234363840
B
A
Vertical Flue Lengths - metres
A = Insulated or within the building
B = Uninsulated and exterior to the building
Draught - Pa
example 1
A single Strata 2-120 boiler is to be installed with a
conventional flue arrangement (taking combustion air
from the plantroom) which takes an all vertical internal
route to roof termination using DN100 flue components.
Length of flue = 10m
Resistance =
10 x 1m lengths DN100 tube @ 7.0Pa = 70
1 x DN100 open termination @ 7.0Pa = 7
Total Resistance = 77Pa
Take into account that 10m of internal vertical flue will
generate approximately 33Pa of draught then final
operating resistance is 77 - 33 = 44Pa
conclusion: Operating resistance is less than 100Pa
therefore no alternative design is required as flue system
has no effect on boiler output.
thermal updraught when
flue gas temp 80°C and outside temp -5°C

11
STRATA2
example 2
A single Strata 2-120 boiler is to be installed with a
room sealed flue using separate air and flue gas tubes
of DN100.
The flue gas tube takes a part horizontal, part vertical
internal route to a roof termination. The air tube takes a
similar route. Flue gas route vertical section = 3m,
horizontal section = 2m. System includes 2 x 90ºbends.
Resistance of flue gas tube =
5 x 1m lengths DN100 tube @ 7.0Pa = 35
2 x DN100 90ºbends @ 7.0Pa = 14
1 x open termination @ 7.0Pa = 7
Flue gas tube resistance = 56Pa.
Take into account 3m of vertical tube will generate 10Pa.
Therefore operating resistance of flue gas tube = 56 –10
= 46Pa.
Now calculate air tube resistance which must be
added to flue gas tube operating resistance to obtain
final resistance.
Air tube length = 6.5m (no consideration is given
to whether vertical or horizontal). System includes
2 x 90ºbends.
Resistance of air tube =
6.5 x 1m lengths DN100 tube @ 4.0Pa = 26
2 x DN100 90ºbends @ 4.0Pa = 8
1 x DN100 termination with rain cap @ 8.0Pa = 8
Air tube resistance = 42
Total operating resistance = 56 + 42 = 98Pa
conclusion: Final operating resistance is less than
100Pa, therefore no alternative design is required as flue
system has no effect on boiler output.
example 3
A single Strata 2-120 is to be installed using 100/150
concentric flue components. The flue route is all
horizontal, to a horizontal wall termination
Length of flue = 4m
System includes 1 x 90ºbend + 2 x 45ºbends.
Resistance =
4 x 1m lengths 100/150 concentric tube @ 12Pa = 48
1 x 100/150 90ºconcentric bends @ 12Pa = 12
2 x 100/150 45ºconcentric bends @ 6Pa = 12
1 x 100/100 to 100/150 concentric adaptor @ 2Pa = 2
1 x 100/150 concentric terminal @ 15Pa = 15
Total resistance = 89Pa.
conclusion: Total flue system resistance is less than
100Pa, therefore no alternative design is required as flue
system has no effect on boiler output.
examples of calculating flue pressure loss
Flue System Resistance - Pa
120
118
116
114
112
110
108
106
104
102
100
98
96
94
92
0 50 100 150 200 250 300 350 400 450
Boiler Output kW at: Flow 50°C Return 30°C
effect of
flue system resistance
on boiler output

12
STRATA2
4.3 flue options & terminal position (contd)
multiple flue system calculation
For flue component resistance for multiple boiler installations refer to graph below.
Volume flue gas per boiler = 170m3/h
Volume combustion air per boiler = 1303/h
Assume resistance of 45°bend = 0.5 tube
Assume resistance of 90°bend or tee = 1.0m tube
150100
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
200 250 300 350 400 450 500 550 600
resistance flue tubes
tube DN125
tube DN150
tube DN200
Resistance - Pa/m
Volume - m3/h
For larger volumes or resistance of alternative tube sizes, contact MHS Boilers Flue Department
flueing possibilities
typical conventional
flue installation.
Air for combustion taken from
the boiler room.
Boiler room MUST be
ventilated in accordance
with BS 6644:1991
flue system layouts

13
STRATA2
flueing possibilities
single boiler room sealed
concentric flue
with horizontal discharge
flueing possibilities
typical room sealed flue
installations - single boiler
flueing possibilities
room sealed flue installation
serving multiple boilers,
where air from combustion is
taken from annular space in
brick chimney
Note: Whereas no ventilation is required for
combustion air when boiler is room sealed,
consideration must be given to general boiler
plant room cooling and it is recommended to
ventilate to provide:- 4.5cm/kW input at
both high and low level direct to outside.
Room
Sealed
Concentric
Room Sealed
Separate Air and
Flue Gas Tubes
1200
min
Note: Whereas no ventilation is required for
combustion air when boiler is room sealed,
consideration must be given to general boiler
plant room cooling and it is recommended to
ventilate to provide:- 4.5cm/kW input at
both high and low level direct to outside.
Air Air
Fall on Flue 3°
Towards Boilers
Inspection
Access
flue system layouts
4.3 flue options & terminal position (contd)
Fig 4.3b
Fig 4.3c
Fig 4.3d

14
STRATA2
Additional Notes for Room Sealed Appliances:
The Clean Air Act Memorandum prevents the use of balanced flue appliances discharging at low level
where the total heat input to the plant room exceeds 150kW. Where the Clean Air Act does not prevent
installation, the following rules must be applied.
Note: Detailed recommendations for flue installation are given in BS5440:1
The following points are for general guidance:
●The boiler must be installed so that the terminal is exposed to external air.
●It is important that the position of the terminal allows free passage of air across it at all times.
●It is essential to ensure that products of combustion discharging from the terminal cannot re-enter the
building or any other adjacent buildings, through ventilators, windows, doors, other sources of natural
air infiltration, or forced ventilation/air conditioning.
●The minimum acceptable dimensions from the terminal to obstructions and ventilation openings are
specified in figure 4.3e.
●If the terminal discharges into a pathway or passageway check that combustion products will not cause
nuisance and that the terminal will not obstruct the passageway.
●Where the lowest part of the terminal is fitted less than 2m (78ins) above ground, above a balcony
or above a flat roof to which people have access, the terminal MUST be protected by a purpose
designed guard.
●Where the terminal is fitted within 850mm (34ins) of a plastic or painted gutter, or 450mm (18ins)
of painted eaves, an aluminium shield at least 750mm long must be fitted to the underside of the
painted surface.
●The air inlet/flue outlet duct MUST NOT be closer than 25mm (1in) to combustible material.
Note: Under most weather conditions the terminal will emit a plume of steam. This is normal but
positions where this would cause a nuisance should be avoided.
In the case of horizontal flue gas discharge pipes, an angle of 3ºmust be observed in the direction of
the boiler (5.0cm for every metre of pipe length) with a fall towards the boiler, to allow condense in the
flue gases to return to the unit.
Minimum dimensions of flue terminal positions:
flue terminal positions
H,I
J
P
A
G
F D
EA
G
P
B,C
F
F
L
K
LK
P
N
4.3 flue options & terminal position (contd)

15
STRATA2
4.4 ventilation requirements
Detailed recommendations for air supply are given in BS 6644:1991. The following notes are for general
guidance. If the combustion air is to be taken from the room in which the unit is located, a guard must be
placed over the air intake to prevent the entry of any foreign bodies.
Room Sealed Installations Only:
If the boiler is to be installed in a cupboard or compartment, permanent air vents may be required for
cooling purposes in the cupboard or compartment. It is essential to ensure that the minimum clearances as
stated in figure 3.2b are maintained.
Water must not be allowed to enter the air intake, as this may affect the performance and behaviour
of the combustion fans.
Dimension Terminal Balanced Flue Non room
Position Room Sealed Sealed
A Directly below an opening, 300mm 300mm
air brick, window etc Not recommended Not recommended
B Below gutters, soil pipes or drain pipes 75mm 75mm
C Below eaves 200mm 200mm
D Below balconies or 200mm 200mm
carport roof Not recommended Not recommended
E From a vertical drain pipe or soil pipe 75mm 75mm
F From an internal or external corner 300mm 200mm
G Above ground, intersecting roof or balcony level 300mm 300mm
H From a surface facing the terminal 2000mm 2000mm
I From a terminal facing the terminal 2000mm 2000mm
J From an opening in the carport 1200mm 1200mm
e.g. door into dwelling Not recommended Not recommended
K Vertically from a terminal on the same wall 1500mm 1500mm
L Horizontally from a terminal on the same wall 300mm 300mm
M From the wall on which the terminal is mounted N/A 50mm
N From a vertical structure on the roof 500mm N/A
P Above intersection with roof 500mm 150mm
4.3 flue options & terminal position (contd)
Table 4

16
STRATA2
4.5 hydraulic system design
Important Note: Strata 2 boilers must only be installed on sealed and pressurised systems. A sealed
system must only be filled by a competent person. Instructions for filling the system are supplied in
section 6.0. A low pressure cut off switch must be installed into the system.
All systems must be thoroughly cleansed prior to the connection of the boiler.
The system water should be treated to prevent general system corrosion and the
deposition of scale or sludge in the boiler waterways. Faliure to observe this
requirement will render all guarantees on the product void. If installing the boiler onto an
old system, it is recommended to install a spirotech or similar dirt arrester/filter.
If plastic pipes are used for the flow and return lines, for radiators or underfloor heating, a plate
exchanger should be considered between the system water and the boiler water. If such a separator is not
used, the MHS guarantee on all boiler parts will become null and void, unless it can be proved that the
plastic pipes used have a vapour tight layer.
The connection of the flow and return are located at the top and the rear of the unit. With regards to
servicing, it is a requirement that isolation valves are installed.
For specialist advice and water treatment products, contact:
Betz Dearborn Fernox, Britannica Works
Widnes, Cheshire WA8 8UD Clavering, Essex CB11 4QZ
Tel: [phone] Tel: [phone]
AAV
Outside Air
Temperature
Sensor
Room Unit
RE3231
Strata 2 - 120
Boiler
Condensate Waste
Low Pressure Switch
Exapnsion Vessel
Filling Point
CWM
DOC
DOC
LSV
IV
SV
IV IV
Strainer
DOC
Return Sensor
Return from
Load Circuits
Temperature
Sensor (Boiler)
Low Velocity
Mixing Header
Max Velocity
0.5m/s
Flow to
Load Circuits
eg. Heating
Circuit
& HWS
Calorifier
To HWS Sensor
recommended system design
typical single Strata 2 - 120 boiler installation
Fig 4.5a

17
STRATA2
AAV
Outside Air
Temperature Sensor
Room Unit
RE3231
Strata 2 - 360
(3 x 120 Boiler)
Condensate
Waste
Low Pressure
Cut Out Switch
Exapnsion Vessel
Filling Point
CWM
DOC
DOC LSV
IV’sIV’sIV’s
SV SV SV
IV IV
Strainer
DOC DOC
Return Sensor
Return from
Load Circuits
Temperature
Sensor (Boiler)
Low Velocity
Mixing Header
Max Velocity
0.5m/s
Flow to
Load Circuits
eg. Heating Circuit
& HWS Calorifier
To HWS Sensor
recommended system design
typical multiple Strata 2 boiler installation
DOC
4.6 gas supply
The Strata 2-120 is designed and set for Natural Gas group G20. The Gas Supplier should be consulted
at the installation planning stage in order to establish the availability of an adequate supply of gas.
An existing service pipe MUST NOT be used without prior consultation with the gas supplier. A gas
meter can only be connected by the gas supplier or by their contractor.
An existing meter and/or pipework should be of sufficient size to carry the maximum boiler input plus
the demand of any other installed appliance. (BS 6891:1988). A minimum of 1”BSP diameter pipework is
required to within 1 metre of the appliance gas cock.
The governor at the meter must give a constant outlet pressure of 20 mbar (8 in. wg) when the
appliance is running.
The gas supply should be purged in accordance with IGE/UP/1&2. WARNING: Before purging open
all doors and windows, also extinguish any cigarettes, pipes and any other naked lights.
4.7 electrical supply
A 240 Volt single phase supply must be present at the proposed boiler location. Wiring external to the
appliance must be in accordance with BS7671 (the current I.E.E. Wiring Regulations) for electrical
installation and any local regulations which apply.
The mains cable must be at least 0.75mm? (24/0.2mm) PVC insulated to BS6500 table 16. The method
of connection to the mains supply must facilitate complete electrical isolation of the appliance. Either a 5A
fused three pin plug and un-switched shuttered socket outlet, both complying with BS1363, or a 5A fused
double pole switch having a 3mm contact separation in both poles and serving only the boiler (and its
external controls) may be used.
WARNING: THIS APPLIANCE MUST BE EARTHED.
(Failure to provide a satisfactory Earth connection would be a safety hazard and may also result in appliance
malfunction).
Fig 4.5b
4.5 hydraulic system design (contd)

18
STRATA2
5.0 installation
intructions
5.1 unpacking the boiler
The boiler is delivered in a palletted carton containing the boiler and associated fittings, plus any other
optional ancillary flue or control components in separate cartons.
The boiler carton contains:
●Fully assembled boiler.
The Strata 2-120 is also delivered with the following items:
●User manual and operating instructions.
●Installation and Servicing instructions for the Engineer.
Built into each unit are the following:
●A gas stop cock for each heat module.
●Three way return water cut-off.
●RVA 47 control unit (master and slave boilers), 1 outside air sensor, 1 flow sensor and 1 return sensor.
The unit must be inspected immediately after delivery. Any damage to the consignments must be
reported within 3 days.
To unpack the boiler, carefully cut away the outer packaging and open the carton top. Lift off the
bottomless carton. By holding the chassis only lift the appliance away from the palette.
To remove the casing from the boiler:
●Remove the two screws on the bottom front edge of the top casing panel.
●Remove panel to the front.
5.2 positioning the boiler
Move the appliance to the desired location, making sure that all clearance dimensions as stated in
section 3.2 are adhered to. Level the appliance in a vertical position by turning the adjustable feet
underneath the base of the unit. Check that the appliance is in a true vertical position by using a spirit level.
Once the appliance is in a true vertical position, the adjustable feet must be secured by locking the nuts.
5.3 air supply and exhaust connections
The unit has two connections, one for the supply of combustion air and the other for the discharge of
the products of combustion. Each connection is clearly labelled and located at the rear top of the appliance.
5.4 gas connection
The Gas connection is located at the rear of the appliance. The gas supply should be sized, installed,
tested and purged in accordance with IGE/UP/1&2.
The connection to the appliance must include a suitable method of disconnection and a gas control
cock must be installed adjacent to the appliance for isolation purposes.
The gas pipe used to supply the appliance must not allow a pressure drop of greater than 1 mbar from
the meter to the appliance. The nominal inlet working gas pressure measured at the appliance should be
20.0 mbar for Nat Gas (G20). The installer should install a pressure test point adjacent to the gas inlet
connection. The gas supply line should be purged.
WARNING: Before purging open all doors and windows, also extinguish any cigarettes, pipes and any
other naked lights.

19
STRATA2
5.5 Water Connections
The central heating flow and return connections are 11/4" BSP male. Two sets of flow and return
connections are provided and located on the rear top of the appliance and the rear of the appliance. The
installer may use both top or both rear connections or one of each for connection of the flow and
return pipes.
A suitable safety valve must be installed onto the boiler flow pipe between the boiler and any
isolation valve. The boiler flow and return pipes must include a method of disconnection and must include
isolation valves.
5.6 condense waste connections
The condense waste connection is located at the lower rear of the appliance. The condense syphon
cleaning point is factory fitted with a heavy grade black plastic cap which MUST NOT BE REMOVED.
Operating the appliance with the cap removed from the syphon cleaning point will allow products of
combustion to be discharged from the cleaning point.
The condense waste connection is a 3/4" BSP male threaded stub fabricated from plastic. The installer
must connect to this stub, a condense waste pipe fabricated from plastic tube and fittings (3/4", 22mm
overflow pipe is considered suitable). Only plastic components must be used for the condensation
discharge. Metal pipes are not acceptable due to the acidic nature of the condensate.
The built in syphon allows the unit to be connected directly to a drain system. If any part of the
condense waste pipe is to be run external to the building or is at risk of freezing, then the pipe must be
suitable insulated to protect from freezing.
If a suitable drain for accepting the condense waste is not available nearby to and below the boiler (e.g.
if the boiler is installed in a basement below ground level), then an (optional extra) condensate receptacle
and pump can be installed into the free space at the base of the appliance. This will collect and remove
condense water to a remote drain up to 5 metres height difference above the receptacle position.
Note: Blockage of the waste discharge will cause the unit to switch off by means of a built in level switch.
When making the condense waste pipe connection to the boiler, do not use adhesives, it is
recommended to lightly apply a suitable jointing tape (PTFE or similar) and use only light pressure to
connect fittings to the appliance to avoid damage to the condense waste outlet assembly. It is
recommended that the condense waste pipework should include a method of disconnection and
cleaning points.
5.7 electrical connections –general
The Strata 2-120 has a number of standard connection points. In addition, a number of panel locations
have been reserved for the installation controller, which can be mounted in the spaces provided after
removing the blank panels.
At the top of the boiler, behind the controllers, is a connector plate stretching across the entire width
of the boiler, flanked by three cable clamp brackets. All electrical connections are made via plugs and
sockets and to avoid mistakes during the connection of the cables, each plug has its own colour.
5.7.1 connecting the power supply
The incoming power supply (230V) must be connected to the black 3 pin Weiland plug located at the
far left hand side of the connectors mounting plate in the top area of the boiler. The unit has a 2-pole
on/off switch for the power supply of the entire boiler and all the connected controllers, pumps and valves.
Determine the cross sectional area of the power supply cable and take into account the power usage
of the combined components connected to the control units.
In addition each burner module has a single pole-switch to switch off one burner unit while the second
unit may continue to function. The main switch is protected by a 6.3 AT fuse.
CAUTION: The main power supply for the boiler must have a higher fuse value.

20
STRATA2
5.7.2 connecting of system safety interlocks
These switches are connected to the ‘dark green’3 pole plug. The central pole provides the common
output (230V AC). The left hand terminal enables the lower module and the right hand terminal enables
the upper module.
5.7.3 connecting remote run indication lamps
Connection points have been provided for the connection of run indication lamps (20W max). See
“Electrical Connection Details”fig 5.7a, for terminal positions.
CAUTION: These outputs must not be linked together as this will result in false lockout being
experienced by the burner control panels.
Legend
PPS. Connection for the Master boiler to a second boiler - Note screened cable must be used .
LPB. Connection for the Master RVA 47 controller to subsequent
RVA 47 controllers -
Note screened cable must be used .
VFO. Connection for the system flow sensor.
SF. Connection for the DHW sensor.
AF. Connection for the outside air sensor.
RE. Connection for the room unit.
HI. Connection for remote enabling volt free or 0-10 Volt control signal.
RFO. Connection for the system return sensor.
SLP. Connection for the DHW 3 way valve or charging pump. (Max 2A).
HKP. Connection for the Heating pump. (Max 2A).
AF1/AF2. Connection for another outside air sensor dedicated for the RVA 46 if required.
If a dedicated sensor is not required the RVA 46 will use the RVA 47 outside air sensor.
RE1/RE2. Connection for the room unit/thermostat dedicated to the RVA 46 VT circuits
VF1/VF2. Connection for the mixed flow sensor of the RVA 46 VT circuits
P1/P2. Connection for the pump of the RVA 46 VT circuits.
M1/M2. Connection for the 3 way mixing valve of the RVA 46 VT circuits.
PPS N L N L AF1 RE1 VF1 AF2 RE2 VF2
LPB VFO SF AF RE H1 RFO
SLP
NE L NE L NEO
HKP P1 M1
NE L NE L NEO
P2 M2
electrical connection details
Run Indication
230 Volt Output
Note: Do Not Link
240V
Supply Fault VF Connections OptionalRemote Safety
Hi/Lo
Interlocks etc
Boiler Power & Communications RVA 47 Boiler Controller Connections RVA 46 VT Controller Connections
Fig 5.7a