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Installation and Servicing
SECTION 4 - FAULT FINDING
4. FAULT FINDING
4.1 DISPLAY FAULTS
Display
Fault
Action
HOT WATER
PREHEAT
OFF
F1
Low Water Pressure
Check system water pressure is between 1 and 1.5 bar on the system
pressure gauge. If system pressure is low top up the CH circuit as per the
steps in Section 2.5. If system pressure is higher than 1.5 bar ensure the
system is cold and carefully reduce the pressure using the draining point
on a system radiator. If fault persists, replace water pressure switch (see
Section 3.15).
HOT WATER
PREHEAT
F2
OFF
No change in DHW
Temperature during
demand period
Ensure primary circuit is correctly pressurised and primed to the correct
operating temperatures. Check primary circuit is fully open and all isolation
valves at base of HIU are open. Ensure all air is purged from primary circuit.
If a CCV (credit control valve) is installed in appliance, ensure dwelling has
sufficient credit to open valve and wiring to valve has good continuity – Refer
to CCV installer and servicing guide for details.
HOT WATER
PREHEAT
OFF
f4
Flow Thermistor
Fault
Remove harness to CH clip on flow thermistor and using a multi-meter
measure the resistance of the thermistor – This should be around 10kΩ in
ambient conditions. If thermistor is functioning correctly reconnect harness
to flow thermistor and reset unit. If thermistor is not functioning correctly
replace item. If fault persists, replace PCB (see Section 3.20).
HOT WATER
PREHEAT
F5
OFF
Return Thermistor
Fault
Remove harness to return to CH clip on thermistor and using a multi-meter
measure the resistance of the thermistor – This should be around 10kΩ in
ambient conditions. If thermistor is functioning correctly reconnect harness
to flow thermistor and reset unit. If thermistor is not functioning correctly
replace item. If fault persists, replace PCB (see Section 3.20).
HOT WATER
PREHEAT
F6
OFF
Outside Sensor
Open Circuit
Remove outside sensor wiring from screw terminals on the back off the HIU
controls enclosure (see Section 2.9 for wiring locations). Using a multi-meter
check resistance and continuity to outside sensor:
At 0°C expect 31,000 - 35,000 Ohms
At 15°C expect 15,000 - 16,500 Ohms
At 30°C expect 7,700 - 8,500 Ohms
If the thermistor has an open circuit or short circuit replace outside sensor
and wiring to outside sensor. Reset the HIU. If problem persists, replace
PCB.
HOT WATER
PREHEAT
F7
OFF
Incorrect Mains
Voltage
Contact a qualified electrician, the building manager, or the electricity
provider.
Continued....
