48 Installation and maintenance instructions Compact 0020313973_01
Code/meaning Possible cause Measure
F.22
System pressure too low
Cable for the pump/for the wa-
ter pressure sensor is loose/not
connected/defective
▶ Check the cable for the pump/for the water pressure sensor.
F.23
Safety switch-off: Temperature
difference too great
Pump blocked ▶ Check that the pump is working correctly.
Air in the product ▶ Purge the heating installation.
Pump runs with insufficient out-
put
▶ Check that the pump is working correctly.
Flow and return temperature
sensor connection inverted
▶ Check the connection for the flow and return temperature
sensor.
F.24
Safety switch-off: Temp. incr.
too fast
Pump blocked ▶ Check that the pump is working correctly.
Pump runs with insufficient out-
put
▶ Check that the pump is working correctly.
Air in the product ▶ Purge the heating installation.
System pressure too low ▶ Check the system pressure.
Non-return valve blocked ▶ Check that the non-return valve is working correctly.
Non-return valve installed incor-
rectly
▶ Check the installation location of the non-return valve.
F.25
Safety shutdown: Flue gas tem-
perature too high
Flue gas safety cut-out plug is
not plugged in or is loose
▶ Check the plug and the plug connection.
Interruption in the cable harness ▶ Check the cable harness.
F.27
Safety switch-off: Flame simula-
tion
Moisture on the PCB ▶ Check that the PCB works correctly.
PCB defective ▶ Replace the PCB.
Gas solenoid valve not leak-
tight
▶ Check that the gas solenoid valve works correctly.
F.28
Ignition unsuccessful
Gas isolator cock closed ▶ Open the gas isolator cock.
Gas meter defective ▶ Replace the gas meter.
The gas pressure monitor has
been triggered
▶ Check the gas flow pressure.
Air in the gas supply (e.g. dur-
ing initial start-up)
▶ Reset the unit once.
Gas flow pressure too low ▶ Check the gas flow pressure.
The thermal isolator device has
been triggered
▶ Check the thermal isolator device.
Condensate discharge pipe
blocked
▶ Check the condensate discharge pipe.
Incorrect replacement gas valve
assembly
▶ Check the replacement gas valve assembly.
Incorrect gas valve assembly
offset
▶ Check the offset setting for the gas valve assembly.
Gas valve assembly defective ▶ Check the gas valve assembly.
Multiple plug loose/not plugged
in
▶ Check the multiple plug and plug connection.
Interruption in the cable harness ▶ Check the cable harness.
Ignition system defective ▶ Replace the ignition system.
Earthing defective ▶ Check the product's earthing.
Electronics defective ▶ Check the PCB.
Air/flue pipe blocked ▶ Check the air/flue pipe.
Restrictor for the reference
pressure pipe blocked
▶ Check the condition of the restrictor on the gas valve
assembly's reference pressure pipes.
F.29
Ignition and check faults during
operation – flame has gone out
The gas supply is interrupted ▶ Check the gas supply.
Incorrect flue gas recirculation ▶ Check the flue gas recirculation.
Earthing defective ▶ Check the product's earthing.
Ignition misfire ▶ Check that the ignition transformer works correctly.
Condensate discharge pipe
blocked
▶ Check the condensate discharge pipe.
Air/flue pipe blocked ▶ Check the air/flue pipe.
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