Vaillant home combi Installation And Maintenance Instructions Manual page 36

Appendix
Fault code Meaning
F.22 Safety switch-off: Low water pressure in
the boiler
F.23 Safety switch-off: Temperature difference
too great (NTC1/NTC2)
F.24 Safety switch-off: Temperature rise too
fast
F.25 Safety switch-off: Flue gas temperature
too high
F.27 Safety switch-off: Fault in flame detection
F.28 Fault: Ignition unsuccessful when starting
up
F.29 Fault: Flame loss
F.32 Fan frost protection function active: Fan
speed outside the tolerance values
F.33 Fan frost protection function active: Air
pressure switch fault
F.49 eBUS fault: Voltage too low
F.61 Fault: Gas valve control system
F.62 Fault: Gas valve switch-off control
F.63 Fault: EEPROM
F.64 Fault: Electronics/sensor/analogue-to-
digital converter
F.65 Fault: Electronics temperature too high
F.67 Value sent back by ASIC is incorrect
(flame signal)
F.68 Fault: Unstable flame (analogue input)
F.70 Invalid product code (DSN)
F.71 Fault: Flow/return temperature sensor
F.72 Fault: Deviation in the water pressure
sensor/return temperature sensor
F.73 Fault: Water pressure sensor not con-
nected or has short-circuited
F.74 Fault: Electrical problem in the water
pressure sensor
F.75 Fault: Pressure sensor
F.77 Fault: Condensate or smoke
F.78 Interruption to DHW outlet sensor at
external controller
36
Possible cause
No or insufficient water in the product, water pressure sensor de-
fective, cable to the pump or to the water pressure sensor loose/not
connected/defective
Pump blocked, insufficient pump output, air in product, flow and return NTC
sensors connected the wrong way round
Pump blocked, reduced pump output, air in product, system pressure too
low, return flow prevention blocked/incorrectly installed
Break in connection for optional flue gas safety temperature limiter (safety
cut-out), break in cable harness
Moisture on the electronics, electronics (flame monitor) defective, gas solen-
oid valve leaking
Gas meter defective or gas pressure monitor has triggered, air in gas, gas
flow pressure too low, thermal isolator device (TAE) has triggered, incorrect
gas restrictor, incorrect spare gas valve, fault on the gas valve, multiple plug
on PCB incorrectly plugged in, break in cable harness, ignition system (ig-
nition transformer, ignition cable, ignition plug, ignition electrode) defective,
ionisation current interrupted (cable, electrode), incorrect earthing of product,
electronics defective
Gas supply temporarily stopped, flue gas recirculation, incorrect earthing of
product, ignition transformer has spark failure
Plug on fan not correctly plugged in, multiple plug on PCB not correctly
plugged in, break in cable harness, fan blocked, Hall sensor defective, elec-
tronics defective
Pressure monitor has not switched or has switched at a fan speed value that
is too high (insufficient air supply)
Pressure monitor plug not correctly plugged in, pressure monitor defective,
line removed from between the pressure monitor and silencer, air/flue pipe
blocked and silencer not installed properly
Short circuit on eBUS, eBUS overload or two power supplies with different
polarities on the eBUS
Short circuit/short to earth in cable harness for the gas valve, gas valve
defective (coils shorted to earth), electronics defective
Delayed switch-off of gas valve, delayed extinguishing of flame signal, gas
valve leaking, electronics defective
Electronics defective
Flow or return NTC short circuited, electronics defective
Electronics overheating due to external influences, electronics defective
Implausible flame signal, electronics defective
Air in gas, gas flow pressure too low, incorrect air ratio, incorrect gas re-
strictor, ionisation flow interruption (cable, electrode)
Replace the screen and PCB at the same time without reconfiguring the
product's Device Specific Number
Flow temperature sensor specifies a constant value: Flow temperature
sensor incorrectly attached to the flow pipe, flow temperature sensor de-
fective
Flow/return NTC sensor temperature difference too great → flow and/or
return temperature sensor defective
Interruption/short circuit of water pressure sensor, interruption/short to earth
in supply line to water pressure sensor or water pressure sensor defective
Line to water pressure sensor has a short circuit to 5 V/24 V or internal fault
in the water pressure sensor
Pressure sensor or pump defective or low water pressure
No response, flue non-return flap defective
Link box connected, but hot water NTC not bridged
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