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Fault Finding & Servicing
Important
•
After servicing, complete the relevant Service
Interval Record section of the Benchmark Checklist
located on pages 22 and 23 of this manual.
•
Servicing should only be carried out by persons
competent in the installation and maintenance of
unvented water heating systems.
•
Any spare parts used MUST be authorised parts.
•
Disconnect the electrical supply before removing
any electrical equipment covers.
•
NEVER bypass any thermal controls or operate
system without the necessary safety valves.
•
Water contained in the cylinder may be very hot,
especially following a thermal control failure. Caution
must be taken when drawing water from the unit.
Fault
No water flowing from
hot taps
Water from hot taps
is cold
Water discharges
from expansion relief
valve
Water discharges
from the T&P valve
intermittently
Water discharges
from the T&P valve
continually
Milky water
Table 5: Fault Finding Chart
Possible cause
1. Mains water supply off.
2. Strainer blocked.
3. Cold water combination valve
incorrectly fitted.
1. Immersion backup heater not
switched on.
2. Immersion backup heater
thermal cut-out has tripped.
3. Programmer set to central
heating only.
4. Heat Pump not working.
5. Heat Pump thermal cut-out has
tripped.
6. Motorised 3 port valve not
connected correctly.
1. Intermittently - charge pressure
in expansion vessel has reduced
or been depleted
2. Continually - 3 bar pressure
reducing valve is not working
correctly.
3. Continually - expansion valve
seat damaged.
1. Charge pressure in expansion
vessel has reduced or been
depleted.
2. 8 bar expansion relief valve
faulty.
1. Thermal control failure. Note:
water will be very hot.
1. Oxygenated water.
Remedy
1. Check and open mains valve.
2. Turn off water supply. Remove strainer in pressure
reducing valve and clean.
3. Check and refit as required.
1. Check and switch on.
2. Check. Reset by pushing button (Figure 08, page 13).
3. Check. Set domestic to a hot water programme. Check
DHW delay settings if high DHW demand usage.
4. Check Heat Pump operation. If fault is suspected
consult Heat Pump manufacturers instructions.
5. Check. Reset by pushing button.
6. Check wiring and/or plumbing connections to motorised
valve. See manual 7841138 for information on wiring
schematics.
1. See page 15 for details on how to test and recharge.
2. Check pressure from 3 bar pressure reducing valve. If
greater than 3 bar replace pressure reducing cartridge.
3. Remove expansion relief cartridge from 8 bar pressure
relief valve and check seating. If necessary fit new
cartridge.
1. See page 15 for details on how to test and recharge.
2. Check valve and replace if necessary
1. Switch off power supply to immersion heater(s) and
shut down the ASHP. DO NOT turn off the water supply.
When discharge stops check all thermal controls, replace
if faulty.
1. Water from a pressurised system releases oxygen
bubbles when flowing. The milkiness will disappear after a
short while.
17
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