Hamworthy DORCHESTER DR35L Guide

IMPORTANT NOTE
THESE INSTRUCTIONS MUST BE READ
AND UNDERSTOOD BEFORE INSTALLING,
COMMISSIONING, OPERATING OR
SERVICING EQUIPMENT
DORCHESTER
DR35L to DR90L-CE
HOT WATER
STORAGE HEATERS
Installation, Commissioning
and Maintenance Instructions

Technical Enquiries 01202 662527/662528
To supplement the detailed technical brochures, technical advice on the application and use of products in the
Hamworthy Heating range is available from our technical team in Poole and our accredited agents.
Site Assembly 01202 662555
Hamworthy offer a service of site assembly for many of our products in instances where plant room area is restricted.
Using our trained staff we offer a higher quality of build and assurance of a boiler built and tested by the manufacturer.
Commissioning 01202 662555
Commissioning of equipment by our own engineers, accredited agents or specialist sub – contractors will ensure the
equipment is operating safely and efficiently.
Maintenance Agreements 01202 662555
Regular routine servicing of equipment by Hamworthy service engineers inspects the safety and integrity of the plant,
reducing the risk of failure and improving performance and efficiency. Maintenance agreements enable our customers to
plan and budget more efficiently.
Breakdown service, repair, replacement 01202 662555
Hamworthy provide a rapid response breakdown, repair or replacement service through head office at Poole and accred-
ited agents throughout the UK.
Spare Parts 01202 662525
A comprehensive spare parts service is operated from our factory in Poole, providing replacement parts for both current
and discontinued products. Delivery of parts and components is normally from stock within seven days. However, a next
day delivery service is available for breakdowns and emergencies.
Customer Services

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NOTE: THESE INSTRUCTIONS MUST BE READ AND UNDERSTOOD BEFORE
INSTALLING, COMMISSIONING, OPERATING OR SERVICING EQUIPMENT.
THIS HEATER IS FOR USE ON 2nd FAMILY GASES ONLY. PLEASE ENSURE RELEVANT
INFORMATION REQUIRED WITHIN DOCUMENT IS FOUND RELATING TO SPECIFIC GAS TO
BE FIRED BEFORE FIRING HEATER.
THIS HEATER HAS BEEN TESTED TO COMPLY WITH THE GAS APPLIANCES
DIRECTIVE (90/396/EEC)
CERTIFICATION No. 0085AP0195-6-8-9
PUBLICATION NO. 500001001
ISSUE ‘G’
October 2003
DORCHESTER
DR35L to DR90L-CE
HOT WATER
STORAGE HEATERS
Installation, Commissioning
and Maintenance Instructions

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CONTENTS
PAGE
1.0 INTRODUCTION AND DELIVERY 1
2.0 DESCRIPTION 1
3.0 GENERAL REQUIREMENTS 1
3.1 Related Documents
3.2 British Standards
3.3 British Gas Publications
4.0 LOCATION 2
5.0 GAS SUPPLY 3
5.1 Service Pipes
5.2 Meters
5.3 Gas Supply Pipes
5.4 Boosted Supplies
6.0 FLUE SYSTEM 3
6.1 Flue Construction
6.2 Waste Gas Volume
7.0 AIR FOR COMBUSTION AND VENTILATION 3
8.0 WATER PIPEWORK INSTALLATION 4
8.1 Installation Layout
8.2 Water Connection
8.3 Safety
8.4 Water Draw Off
8.5 System Checks
9.0 GAS PIPEWORK INSTALLATION 4
10.0 ELECTRICAL CONNECTION - HEATER 4
11.0 CONTROL SYSTEM 5
11.1 Control Thermostat
11.2 Limit Thermostat
12.0 COMMISSIONING 5
12.1 Checks
12.2 Procedure for Lighting
12.3 Combustion Checks

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PAGE
13.0 SERVICING 6
13.1 Removal of Gas Train
13.2 Burner Assembly
13.3 Servicing the Pilot Burner
13.4 Pilot Burner Checks
13.5 Cleaning Flue Gas Passageways
13.6 Inspecting Inside of Heater
13.6.1 Draining the Heater
13.6.2 Removal of Inspection Door
14.0 RECOMMENDED SPARES 8
15.0 STORAGE TANKS 8
15.1 Location
15.2 Installation
15.3 Assembly of Thermostats
15.4 Connection of Pump Minimum Thermostat
15.5 Pipework Schemes
15.6 Water Connections
15.7 Electrical Connections - Storage Tank
15.8 Storage Tank Thermostat
15.9 Loading Pump
15.10 Operation
15.11 Servicing
FIGURES PAGE
Figure No. 1 Sectional View DR35L-90L Water Heater 10
Figure No. 2 Dimensioned Views 11
Figure No. 3 Installation - Single DRL Heater 12
Figure No. 3A Installation - Multiple DRL Heaters 12
Figure No. 4 Electrical Schematic Diagram 13
Figure No. 5 Honeywell Softlite Control Valve 14
Figure No. 6 Pilot Burner 14
Figure No. 7 Installation of DRL Heater with Storage Tank 15
TABLES
Table 1 Technical Data 2
Table 2 Waste Gas Data 3
Table 3 Air Requirements 4
APPENDIX 1 CORREX CORROSION PROTECTION 16
APPENDIX 2 ADJUSTMENT FOR LPG USAGE 21
APPENDIX 3 UNVENTED SYSTEMS 25
APPENDIX 4 FULLY AUTOMATIC / NATURAL GAS 28

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1.0 INTRODUCTION AND DELIVERY
1.1 This heater must be installed by a competent
person holding ‘CORGI’ registration or equivalent.
All installations must conform to the relevant Gas
Safety and Building Regulations. H.S.E. requirements
must also be taken into account when installing any
equipment.
Failure to comply with the above may lead to
prosecution.
1.2 This heater is intended for use on Natural Gases
(Family 2) only. For LPG (3rd Family gases), a
different model is required. Please consult the heater
data plate to ascertain which gas group the heater has
been manufactured to use. Heaters MUST NOT use
gas other than for which it was designated and made
for.
1.3 All heaters are factory assembled and delivered
individually packed and shrouded in polythene on a
wooden pallet with a separate draught diverter.
The exterior casing of the heater is coated with a
protective plastic coating which should be peeled off
following installation.
To check the size of the heater, refer to the rating
label which is attached to the heater casing and
mounted directly above the junction box assembly.
2.0 DESCRIPTION
The Hamworthy DRL series is a range of fully
automatic hot water storage heaters with Permanent
Pilot ignition, designed exclusively for the preparation
of hot water and fired by a number of atmospheric
multi-gas stainless steel burner bars. The gas control
valve and burner bars can be removed from the
heater as a complete gas train assembly, being
mounted above a tray and positioned beneath the
combustion chamber at the base of the heater. The L
range has been specifically designed to meet the
exacting requirements of the DHSS Code of Practice
for the prevention of Legionellae.
Flue gases from the combustion chamber enter the
draught diverter via a number of vertical fire tubes
which are individually retarded to ensure maximum
heat transfer to water. The draught diverter must be
fitted to the heater in an unmodified condition and
provides a horizontal flue outlet connection which is
adjustable through 360° in the horizontal plane. The
diverter locates on a spigot on the heater flue
connector dome and is secured with a stainless steel
fixing clamp.
The interior vessel of the heater consists of a fully
welded, convexed bottomed, pressure tested, storage
vessel which is thermoglazed with a high quality glass
lining on all waterside surfaces. This, together with
two removable sacrificial anodes, provides the best
possible protection against corrosion. This vessel is
fully insulated and is covered by sheet steel casing. A
parasitic current anode system (non-sacrificial) is
available for those regions of the United Kingdom
where water conductivity is less than 200 micro-
siemens per centimetre - see Appendix 1. The
connections provided are cold water inlet, hot water
outlet, re-circulation, drain cock and inspection/
cleaning outdoor. A 2” BSP socket is available for
combined temperature/pressure relief valves required
on unvented systems - see Appendix 3.
All screw threads used in the Water Heater conform to
the following:-
ISO 7/1 or ISO 228/1 for pipe threads where
applicable.
ISO 262 for all general screw threads.
Automatic water outlet temperature regulation is by
means of a control thermostat which, for normal
operation, should be set to a value not exceeding 60°
C. Overheat protection is provided by a limit
thermostat, with thermal reset.
The heaters manufactured in four sizes, DR 35L, DR
50L, DR 70L, DR 90L, are floor mounted and are
designed for providing hot water for commercial and
industrial premises (refer to Table 1 for technical
data). They can be installed in single or multiple units.
3.0 GENERAL REQUIREMENTS
3.1 Related Documents.
Gas Safety Installations and Use Regulations 1994.
It is Law that all gas appliances are installed by
competent persons 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 this law is complied
with.
1

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MODEL DR35L DR50L DR70L DR90L
Input (Gross) 43 kW 62 kW 87 kW 111 kW
Output 34 kW 49 kW 69 kW 88 kW
Weight (filled) 534 kg 539 kg 549 kg 570 kg
Maximum working head 53m 53m 53m 53m
Nominal inlet gas pressure to the Appliance 20 mbar 20 mbar 20 mbar 20 mbar
Maximum gas inlet pressure 25 mbar 25 mbar 25 mbar 25 mbar
Gas burner operating pressure 12.3 mbar 12.7 mbar 12.3 mbar 13.2 mbar
Injector diameter 3.6 mm 3.5 mm 3.6 mm 3.6 mm
Injector marking 360 350 360 360
Number of burner bars 2 3 4 5
Nominal flue size (dia) 130 mm 150 mm 175 mm 225 mm
Capacity 325 litres 315 litres 300 litres 280 litres
Recovery rate raised through 44° C (80° F) 658 l/h 950 l/h 1336 l/h 1713 l/h
IM/5 - Soundness testing procedures for industrial
and commercial gas installations.
IM/11 - Flues for commercial and industrial gas fired
boilers and air heaters.
IM/16 - Guidance notes on the installation of gas
pipework, excluding domestic installations of 25 mm
and below.
4.0 LOCATION
The heater location should be such that a satisfac-
tory flue system can be connected. An adequate air
supply must be provided for combustion and ventila-
tion and sufficient space for servicing provided.
The heater must be installed on a level concrete
floor or plinth which is sufficient to support its weight
when filled with water (reference Table 1).
Any combustible material adjacent to the heater and
flue system must be so placed or shielded as to en-
sure that its temperature does not exceed 65° C
(150° F).
The installation of the heater MUST be in accor-
dance with the relevant requirements of the Gas
Safety Regulations, Building Regulations, IEE Regu-
lations and the byelaws of the local water undertak-
ing.
It should also be in accordance with the relevant re-
quirements of the local gas region and local author-
ity and the relevant recommendations of the follow-
ing documents:-
3.2 British Standard Codes of Practice
BS 6891 - Installation of low pressure gas pipework
of up to 28 mm (R1) in domestic premises. For lar-
ger installations see IM/2, IM/5 and IM/16 below.
BS 6644 - Installation of gas fired hot water boilers -
60 kW to 2 MW.
BS 6700 - Design, installation, testing and mainte-
nance of services supplying water for domestic use.
BS 6880 - Part 1, 2 and 3 Code of Practice for low
temperature hot water heating systems of output
greater than 45 kW.
CP 342 - Centralised hot water supply, Part 2 -
buildings other than individual dwellings.
BS 3456 - The testing and approval of domestic
electrical appliances Part 1 Clause 27.3.
3.3 British Gas Publications
IM/2 - Purging procedures for non-domestic gas in-
stallations.
Table 1. Technical Data

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Flue systems must be designed in accordance with
the current regulations and with reference to the Brit-
ish Gas publication ‘Flues for Commercial and Indus-
trial Gas Fired Boilers and Air Heaters’. The Following
points should be noted:-
6.1.1 The heater must have its correct draught di-
verter fitted in an unmodified condition before connec-
tion into the flue system.
6.1.2 The flue system must be self-supporting - refer
to Fig. 1
6.1.3 The heaters must be located as near to the flue
or flue header (on multi-bank installations) as possi-
ble. The distance between the heaters and the chim-
ney must not exceed 2 m (6 ft).
6.1.4 The flue system must be designed to achieve a
minimum suction of 0.05 mbar (0.02” wg) at the
draught diverter outlet. 0.05 mbar (0.02” wg) is
equivalent to 1.5 metres of vertical flue. The flue con-
nection on the heater is intended for sheet metal flues.
In some instances mechanical assistance may be
necessary, refer to British Gas publication ‘Flues for
Commercial and Industrial Gas Fired Boilers and Air
Heaters’.
6.1.5 The materials for the flue system must be non-
combustible, mechanically robust and resistant to in-
ternal and external corrosion.
6.2 Waste Gas Volume and Temperatures
It is recommended that the volume and temperature of
the exhaust gases used for the design of the flue sys-
tem is as shown below:-
5.0 GAS SUPPLY
5.1 Service Pipes
The local gas region must be consulted at the installa-
tion 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 local gas region.
5.2 Meters
If necessary a new gas meter will be connected to the
service pipe by the local gas region, or a local gas re-
gion contractor.
5.3 Gas Supply Pipes
Supply pipes must be fitted in accordance with BS
6891. Pipework from the meter to the heater must be
of adequate size and not smaller than the heater gas
connection (¾” BSP).
5.4 Boosted Supplies
Where it is necessary to employ a gas pressure
booster, the controls must include a low pressure cut-
off switch at the booster inlet. The local gas region
must be consulted before a gas pressure booster is
fitted.
6.0 FLUE SYSTEM
6.1 The Hamworthy DRL Series Hot Water Heaters
are designed to be used with natural draught flues.
TABLE 2. Waste Gas Data
Exhaust Gas Volume
at N.P.T
Nett Exhaust
Gas Temp
m3/h ft3/h °C °F
DR 35L 67 2350 190 374
DR 50L 90 3187 245 473
DR 70L 120 4260 214 418
DR 90L 161 5696 200 302
Heater Model
Note: Aerosols in hairdressing salons give off va-
pours as do some industrial processes which can
cause rapid corrosion of heater components. It is
therefore essential that in these instances combustion
air must be ducted from a space where vapours are
not present.
7.0 AIR FOR COMBUSTION AND VENTILATION
Adequate air for combustion and ventilation must be
provided by means of openings at high and low level
within the boilerhouse. The air supply requirements
specified in BS 6644 are summarized as follows:-

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9.0 GAS PIPE INSTALLATION
Fit the ¾” gas cock and nipple provided to the inter-
nal ¾” BSP union connection at the inlet of the gas
control valve.
NOTE: The union has parallel machined faces with
an integral seal. Before connecting the main gas
supply, unscrew the two separate halves of the un-
ion and check that the seal is in position before re-
assembly.
DO NOT CONNECT THE MAIN GAS SUPPLY
WITHOUT ENSURING THE SEAL IS IN POSI-
TION.
Connect the incoming gas supply to the gas cock on
each heater, observing the notes detailed in para-
graph ‘Gas Supply’ and conforming to the require-
ments of BS 6891. Before commissioning the com-
plete gas installation must be purged, inspected and
pressure tested for soundness.
NOTE: Do not run the gas pipework across the front
of the heater since this will prevent removal of the
gas train assembly for cleaning.
10.0 ELECTRICAL CONNECTION - HEATER
WARNING: THIS APPLIANCE MUST BE
EARTHED.
Electrical supply required is 230 volts, 50 Hz, single
phase fused at 5 amps.
The method of connection to mains electrical supply
should facilitate complete isolation for the heaters
and should be provided in a readily accessible posi-
tion.
The wiring must be completed in heat resistant three
core cable sized 1 sq mm CSA.
The method of connection is as follows:-
Remove control thermostat knob and then front
cover to expose PC board and terminal rail. Pass
supply cable through one of the glands provided and
connect live, neutral and earth wires to the appropri-
ate terminals marked LI, N and earth.
The earth wire should be so cut that it is longer than
the live and neutral wires to comply with the require-
8.0 WATER PIPEWORK INSTALLATION
8.1 For details of a typical installation scheme of a
DRL water heater refer to Fig. 3. For details of a
typical installation scheme of multi-DRL water
heater refer to Fig. 3A.
8.2 Water Connections
Cold water feed - 1½” BSP female socket.
Hot water outlet - 1½” BSP female socket.
Secondary connection - ¾” BSP female socket.
8.3 The hot water flow pipe each heater must be fit-
ted with a relief valve ¾” in diameter (20 mm) and
an open vent 1¼” in diameter (32 mm). The vent
should rise to discharge over the feed cistern. No
isolating valves should be fitted between the water
heater and the draw-off point for relief valve and
vent. For unvented systems see Appendix 3. The
maximum working head of the heater is 53 m (174
cu ft).
8.4 Dead legs to water draw-off points should be as
short as possible and in no case should they exceed
the lengths laid down in the Water Byelaws. The
Water Byelaws state that the maximum lengths of
pipe supplying a hot water draw-off tap measured
along the axis of the pipe from the heater, cylinder
or tank or from a secondary circuit are as listed be-
low:-
Pipes not greater than 19 mm ID - max dead leg
length 12 m.
Pipes in range 10-24 mm ID - max dead leg length
7.6 m.
Pipes greater than 25 mm ID - max dead leg length
3 m.
8.5 After installation of the water system has been
completed, open the main water supply valve, flush
the system and fill the heater. Open the hot water
taps and allow air to escape from the system. When
the system is free of air close the hot water taps and
check for leaks on all the water heater connections
including the drain cock and control and limit ther-
mostat pockets.
Low Level (Inlet) 540 cm² plus 4.5 cm² per kW in excess of 60 kW
total rated input
High Level (Output) 270 cm² plus 2.5 cm² per kW in excess of 60 kW
total rated output.
TABLE 3—Air Requirements
NOTE: High level is considered to be as close to the roof as possible. Low level is considered to be 6”
above floor level.

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ments of BS 3456 Part 101 Clause 27.3
NOTE: If a DRL heater is to be used in conjunction
with a Storage Tank, further wiring will be required
to complete the circuitry for the storage tank thermo-
stat and loading pumps. Therefore refer to para-
graph ‘Electrical Connections - Storage Tank’.
11.0 CONTROL SYSTEM
11.1 Control Thermostat.
The hot water outlet temperature is regulated by a
single control thermostat (B1N) which senses, via a
pocket, the heater water temperature and is located
at the top front of the heater as detailed in Fig. 1.
The thermostat contacts normally closed are con-
nected in series with the main live supply to the
Honeywell gas valve and earthed back to earthing
terminals within the heater junction box - see Fig. 4.
The control thermostat is graduated for a 35°C to
90°C operation but to comply with Hamworthy rec-
ommendations the outlet temperature should be
regulated up to a maximum of 60°C. The thermostat
is fitted with an internal stop, restricting the settings
between 35°C and 60°C.
11.2 Limit Thermostat
A fixed 85°C thermostat (B1F) is pre-wired in series
with the pilot flame thermocouple via a thermocou-
ple interrupter - reference Fig. 4 and 5. In the event
of the thermocouple interrupter limit thermostat be-
ing activated, the flame signal from the pilot thermo-
couple to the Honeywell valve is broken, both the
pilot and the main flame are then extinguished and
the heater shuts down under a lockout condition.
The limit thermostat is the thermal resetting type,
but the heater will not re-fire until the pilot flame is
re-established as detailed in the commissioning in-
structions under the paragraph ‘Commissioning’.
NOTE: In the event of the overheat limit thermostats
being activated, the complete heater installation
should be inspected to trace and isolate the cause
of the problem before any further firing takes place.
12.0 COMMISSIONING
12.1 Checks
Before attempting to commission any heater ensure
that any personnel involved are aware of what ac-
tion is to be taken and begin by making the following
checks:-
a) Flueway passages to the chimney are clear.
b) Adequate ventilation exists in the boiler-
house - reference Table 3.
c) The system is vented fully charged with water
and ready to receive heat.
d) The gas supply pipework is clear of any loose
matter, tested for soundness and purged.
e) Gas supply is connected but turned off, gas
cock is closed, unions are tightened (with any
seals in position), test points are tight, burners
are correctly positioned, injectors are tight
and the pilot is connected from the control
valve.
f) Electricity is connected, but ensure that the
supply is switched off.
12.2 Procedure for Lighting (Permanent Pilot Igni-
tion)
Turn control thermostat to the minimum setting (35°
C) and ensure electrical supply is off.
Open heater gas cock.
Depress fully start button (white) on gas valve
(allowing gas to pass to the pilot burner) and ignite
burner by repeatedly pressing the Piezo electric ig-
nitor.
When the pilot is alight, maintain the start button de-
pressed for a further twenty seconds, allowing ade-
quate current to be generated by the thermocouple
to hold the pilot valve open.
If the pilot does not light, re-vent the gas lines to out-
side the building and check whether gas is present
at the pilot. The start button must be fully de-
pressed.
Having established the pilot, release the start but-
ton, remove the pilot adjustment cover screw on the
valve - see Fig. 5 - and adjust the screw beneath to
give a pilot flame envelope of 12 mm (0.5”) long
around the thermocouple.
After pilot adjustment, check that any electrical cir-
cuits are closed and switch on the power supply to
the appliance. Adjust the control thermostat to the
recommended required setting (to a value not ex-
ceeding 60°C) after which the gas valve will open
and the main burner will light.
After the heater has operated for approximately five
minutes, switch off power, slacken the gas pressure
test point, screw on the Honeywell valve - see Fig.
5 - and fit a manometer. Switch the heater on and
measure the operating gas pressure. Check read-
ings against pressure required in Table 1. Adjust
control valve regulator as necessary by removing
cap and using a screwdriver, turning the nylon ad-
justing screw beneath clockwise to increase, anti-
clockwise to decrease the pressure. Switch off
burner by isolating power supply.
Remove manometer, remembering to re-tighten
pressure test point. Relight the burner and check
that no waste gas spillage occurs from any draught
diverter. Check operation of control thermostat by

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Slacken the screw retaining the plastic cover over
the gas valve operator terminals - reference Fig. 5.
Remove the cover, pull off the live and neutral
spaded connectors and then disconnect the
earthing cable from the posidrive clamping screw.
The gas train assembly is secured to the heater by
two nuts on front feet and screw behind the Piezo
igniter. Removal of these enables the assembly to
be withdrawn (care should be taken on removal of
this assembly to avoid damage to the Piezo ignition
unit).
13.2 Burner Assembly
The individual burner bars are attached to the gas
manifold by three No. 8 x ⅜” long self-tap screws
and U type captive nuts. Each burner can be re-
moved and checked for cleanliness to ensure that
the burner venturis, main injectors and flame ports
are free from the accumulation of dust and debris. If
necessary, clean and brush. If main injectors are
removed for cleaning, ensure they are fitted to the
burner manifold with the new copper sealing wash-
ers - refer to the spares list.
13.3 Servicing Pilot Burner
Thermocouple - check thermocouple for any signs
of flame erosion and change as necessary.
Electrode - check electrode for cracks in ceramic or
flame erosion at ignition tip and change as neces-
sary.
Cleaning - release the nut securing the gas connec-
tion to the pilot burner and withdraw the pilot injec-
tor. Check to ensure that the pilot injector burner
flame ports and the air injectors are free from the
accumulation of dust by blowing through as neces-
sary.
Replace in reverse order.
13.4 Pilot Burner
Inspect the two port pilot burner and thermocouple
assembly. If the pilot is heavily contaminated with
dust, clean the flame ports and if necessary remove
the pilot orifice from the pilot burner as detailed in
Fig. 6. If the thermocouple shows any signs of wear
from flame or erosion, replace it immediately.
Check the operation of the Piezo electric ignition
system. Repeated pressing of the Piezo ignitor
should generate a spark between the electrode and
the pilot burner flame port. If no spark is visible
check for damage to the Piezo electric generator,
the Piezo cable (possible fracture) and the spark
electrode (possible crack in ceramic) and replace
as necessary.
6
adjusting temperature setting, thus lighting and ex-
tinguishing the main flame.
12.3 Combustion Check
A flue gas sampling point is not provided. However,
access to the primary flue is available via the
draught break in the draught diverter hood. There-
fore to obtain a full gas analysis it will be necessary
to utilise a U shaped sampling tube, passing through
the draught diverter into the main gas stream.
For natural gas only:-
Normal CO2= 8% - 9% by volume.
Normal CO level should not exceed 200 ppm by vol-
ume.
All for a dry gas sample.
Upon satisfactory completion and testing explain to
the user the method of economic and efficient op-
eration of the system. Ensure that the user is fully
conversant with the lighting, shutting down and gen-
eral operating procedure.
13.0 SERVICING
IMPORTANT: Due to the variable chemical nature
of distributed water supplies, it is recommended that
in addition to the annual inspection cleaning, this
appliance is inspected for calcium deposition anode
loss within a maximum of three months following
initial commissioning and the frequency of subse-
quent inspections adjusted accordingly.
Failure to install in accordance with the relevant
Hamworthy Heating Installers Guides and to
carry out the above recommendations may compro-
mise appliance warranties.
Regular annual servicing is recommended. Although
cleaning of the flueways may not be necessary
every year, it is important that all controls and safety
features are checked for correct operation.
WARNING: Before proceeding with any mainte-
nance, isolate the electrical supply and turn off the
gas service cock to the heaters being serviced.
13.1 Removal of Gas Train
Unscrew and disconnect the two halves of the ¾”
gas pipework union at the inlet to the gas valve and
remove and retain the union rubber sealing ring.
Pull off the sleeved spaded thermocouple interrupter
leads linking the limit thermostats to the thermocou-
ple interrupter assembly on the gas valve. The inter-
rupter leads are identifiable as blue and black wires.
Remove the three core power supply lead to the gas
valve as follows:-

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NOTE: If the gas passages are to be cleaned pro-
ceed to the following paragraph before replacing the
gas train assembly.
13.5 Cleaning Flue Gas Passageways
Access to the heater flueways will require removal
of the draught diverter, the top cover ring of the
heater casing and the flue collector dome.
Before removing the draught diverter ensure that the
main flue system is self-supporting. Slacken and re-
move the two set screws retaining the draught di-
verter fixing clamp, remove the clamp and lift the
draught diverter horizontally away and clear of the
main flue.
Remove the four screws retaining the top cover ring
of the exterior heater casing, lift the ring clear of the
heater and remove the top insulation sections to ex-
pose the flue collector dome and the magnesium
anodes.
Remove the four screws retaining the flue collector
dome and lift the dome clear of the heater.
Withdraw each of the suspended flue gas retarders
vertically upwards and clear of the firetubes.
NOTE: For heaters installed in buildings with mini-
mum clearance for maintenance - reference Fig.2, it
may be necessary to flex the retarders as they are
withdrawn.
Inspect each of the vertical firetubes and if there is
any scale or extraneous deposits, clean each tube
through with a stiff brush and collect any debris in
the condensate tray and replace flue gas dome in
reverse procedure. Check rope seal and replace as
necessary.
NOTE: If anodes are to be inspected proceed to the
next paragraph before replacing insulation, top cas-
ing ring, draught diverter and gas dome.
13.6 Inspection of the Heater Waterside Surfaces
and Magnesium Anodes
13.6.1 Draining the Heater
Isolate the cold feed, hot flow and circulation con-
nections and three way vent if more than one
heater. Connect a ¾” nominal bore hose to the drain
cock connection at the bottom right hand side of the
heater, run the hose to a convenient drainage point,
open the heater drain cock and drain the heater.
13.6.2 Removal of Inspection Door
After checking to ensure that the heater has been
fully drained, remove the four screws retaining the
exterior (blue) casing panel of the inspection door.
Remove the panel and the insulation disc to expose
the inspection door flange and fixing bolts. Slacken
and remove the M10 bolts and take off the inspection
door.
Inspect the interior surfaces of the heater for any
signs of calcium deposit.
Providing that exit water flow temperature has been
restricted to a maximum of 60°C deposits should not
normally be present. If any deposits do exist within
the heater, these can be removed with the aid of a
stiff brush and a water jet (directed through the in-
spection port) and flushed through the drain connec-
tion of the heater.
NOTE: On no account should a metal scraper be
used to remove deposits since this may result in
damage to the glass lining.
After cleaning, replace the inspection door and gas-
ket.
13.7 Inspection of Magnesium Anodes
NOTE: On no account remove the magnesium an-
odes without checking to ensure that the heater is
isolated on flow, feed and circulation waterside con-
nections.
Each heater includes sacrificial magnesium anodes
which hang vertically within the heater water jacket
and are located in ¾” BSP sockets at the top of the
heater casing - reference Fig. 1.
Release the nuts securing the magnesium anodes
(this will require a 30 mm socket spanner complete
with extension bar) and withdraw the anodes verti-
cally through the ¾” BSP sockets and clear of the
heater. Remove the copper anode sealing washer
and inspect each anode for erosion. If the extent of
erosion is sufficient to have reduced the cross-
sectional area of the anode by fifty percent I.e. the
diameter of the anode is less than 15 mm, it should
be replaced complete with a new sealing washer.
13.8 Assembly - Following Complete Servicing of the
Heater.
Close the heater drain cock and remove the hose
connection.
Open the heater cold feed, hot flow and circulation
isolation valves and three way vent valve if fitted. Al-
low the system to fill with water.
Check to ensure that there are no leaks from the in-
spection door sealing gasket, the magnesium anode
sealing washers and the drain cock.
Replace the insulation disc over the inspection door
flange and refit the exterior casing panel with the four
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Replace the gas dome (renew rope seal if neces-
sary), the insulation ring at the top of the heater and
re-attach the top cover ring, draught diverter and
diverter fixing clamp in reverse procedure to that de-
tailed in the paragraph headed ‘Cleaning Flue Pas-
sageways’.
Slide the serviced gas train assembly beneath the
heater. Reconnect the electrical connections to the
gas valve, the gas manifold fixing screws and the ¾”
gas pipework union (complete with the rubber seal)
in the reverse procedure to that detailed in the para-
graph headed ‘Removal of Gas Train’.
14.0 RECOMMENDED SPARES
14.1 Description Part No.
Multi-functional control valve ¾ V4410 531907007
Control thermostat 747440052
Limit thermostat 533901190
Thermocouple 339008149
Thermocouple interrupter assembly 339008198
Main injector - DR 35L - 70L - 90L 532902004
Main Injector - DR 50L 330512495
Washer - main injector (copper) 339008347
Pilot injector (natural gas) - DR 35L - 90L 331101694
Pilot burner assembly (natural gas) complete 330514038
Piezo electric ignitor complete with ignitor cable 339008073
Main burner bar - DR 35L - 90L 333811134
Inspection door sealing gasket 339008966
Washer - magnesium anode (copper) 331604911
Magnesium anode 539001014
15.0 STORAGE TANKS
The Dorchester range of DRL Water Heaters can be
coupled to one or more storage tanks on installa-
tions which require the use of large volumes of wa-
ter over short periods.
The following sections detail a typical method of
coupling the heater and tank together using a ther-
mostatically controlled loading pump (not Hamwor-
thy Heating supply) to transfer hot water from the
heater to the storage tank, and additional thermo-
stats (see Figs 4 and 7).
NOTE: The installation of the storage tank must be
made in accordance with the relevant British Stan-
dard Codes of Practice detailed in the paragraph on
‘Related Documents’, and be suitable for the system
pressure.
15.1 Location
The storage tank must be installed on a level floor or
plinth which is sufficient to support the weight when
filled with water.
15.2 Installation
NOTE: When a DRL water heater is used in con-
junction with a storage tank the modifications de-
tailed in the following two paragraphs must be com-
pleted before connecting the mains electrical supply
to the heater or charging the system with water.
15.3 Assembly of Thermostats B2N and B3N
(reference Fig. 4).
When a storage tank is coupled to the heater pump
minimum thermostat B2N must be fitted in the con-
trol housing and its capillary led to a thermostat
pocket which replaces plugged tapping 24 Fig. 1.
Pocket ¾” BSP - Part No. 531050005
B2N thermostat - Part No. 747440086
15.4 Connection of Pump minimum Thermostat
(reference B2N)
The base plate housing the control and limit thermo-
stats must be carefully removed to enable fitment of
the additional thermostat.
a) Disconnect wiring to thermostat B1N and B1F
and flying earth lead to base plate.
b) Remove screws securing base plate to main
control housing.
c) Carefully ease thermostat capillaries through
control housing bush whilst removing base
plate sufficiently far enough to gain access to
the rear.
d) Assemble pump minimum thermostat to the
base plate, using the screws provided, ensur-
ing that it takes up its position to the left of the
control stat with spade connections facing up-
permost.
e) Ease capillary and bulb through control hous-
ing bush and insert into lower pocket. Surplus
capillary length can be carefully enclosed in

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the electrical trunking alongside
f) Secure base plate to control housing and en-
sure that the earth lead connection is made.
g) Reconnect wiring to thermostats B1N and
B1F
h) Remove link connecting the two flying leads
to the left hand side of the PCB.
i) Connect these leads to the new thermostat
B2N ensuring that they contact the left and
centre spade connections (Common and Nor-
mally open)
j) Remove clear plastic cover and set thermo-
stat to desired setting - normally 55°C.
k) Replace control housing cover and thermostat
knob
In addition a loading pump thermostat B3N and ½”
BSP pocket is fitted into the storage tank and wired
back to the heater control housing as described un-
der ‘Electrical Connection’ below.
B3N thermostat including pocket - Part No.
747433776
15.5 Pipework Schemes
For details of typical installation schemes of a DRL
heater used in conjunction with one Storage Tank
refer to Fig. 7.
15.6 Water Connections
The hot water flow pipe for each tank must be fitted
with a relief valve ¾” in diameter (20 mm) and an
open vent 1¼” in diameter (32 mm). The vent
should rise to discharge over the feed cistern. No
isolating valves should be fitted between the water
heater and the draw off point for the relief valve and
vent.
After the installation of the water system has been
completed, open the hot water taps and allow air to
escape from the system. When the system is free of
air, close the hot water taps and check for leaks on
all storage tank connections including the ther-
mometer and control thermostat pockets.
For unvented systems see Appendix 3.
15.7 Electrical Connections - Storage Tank
The lower thermostat, designated Minimum B2N
Pump Thermostat, must be wired so that the Nor-
mally Open contact is in series with the loading
pump - reference terminals 14 and 9, Fig. 4.
The wiring should also include an earth connection
back to the heater terminal rail.
15.8 Storage Tank Thermostat.
The thermostat in the Storage Tank - ref. Fig. 4 -
designated the Loading Pump Thermostat B3N,
must be wired so that the Normally Closed contact is
in series with the loading pump - reference terminals
9 and 10, Fig. 4. The wiring should also include an
earth connection back to the heater terminal rail.
15.9 Loading Pump
Connect a live, neutral and earth supply to the load-
ing pump via a 3 core 1 mm CSA cable run from ter-
minal rail.
NOTE: When wiring both thermostats and the load-
ing pump, access to the heater terminal rail is via the
heater trunking cover and the spare compression
gland fittings in the heater junction box assembly.
15.10 Operation
Assuming the required exit flow temperature deliv-
ered from the storage tank is 60°C, the settings of
the heater control thermostat, the pump minimum
thermostat and the loading pump thermostat would
be typically 60°C, 55°C and 60°C respectively.
During initial light-up (with both the heater and stor-
age tank filled with cold water) the burner ignites and
raises the water within the heater to the required
control temperature. As the water in the heater
reaches 55°C the pump is energised and transfers
hot water from the heater to the storage tank. This
will result, initially, in a mixed water temperature
which will be less than 55°C and therefore the pump
will stop, and heater continues to fire up to 60°C. The
process will continue until both the heater and stor-
age tank are filled with hot water at 60°C.
During draw-off, the hot water delivered from the
storage tank is displaced by hot water from the
heater, which is similarly replaced by cold water from
the feed cistern. The addition of cold water into the
heater is sensed and provides immediate re-heating
at full rated output. Therefore, the combination of the
heater and storage tank thermostats ensures that the
storage tank is maintained charged full with hot wa-
ter at all times.
15.11 Servicing.
The storage tank should be serviced to the instruc-
tions supplied by the manufacturer.

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