Appendix
34 Installation and maintenance instructions SUSTAIN ..s 0020200967_00
Fault code Meaning Possible cause
F.20 Safety switch-off: Overheating temperat-
ure reached
Incorrect earth connection between cable harness and product, flow or return
NTC defective (loose connection), black discharge via ignition cable, ignition
plug or ignition electrode
F.22 Safety switch-off: Low water pressure in
the boiler
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
F.23 Safety switch-off: Temperature difference
too great (NTC1/NTC2)
Pump blocked, insufficient pump output, air in product, flow and return NTC
sensors connected the wrong way round
F.24 Safety switch-off: Temperature rise too
fast
Pump blocked, insufficient pump output, air in product, system pressure too
low, non-return valve blocked/incorrectly installed
F.25 Safety switch-off: Flue gas temperature
too high
Break in plug connection for optional flue gas safety temperature limiter
(STB), break in cable harness
F.27 Safety switch-off: Fault in flame detection Moisture on the electronics, electronics (flame monitor) defective, gas solen-
oid valve leaking
F.28 Fault: Ignition unsuccessful when starting
up
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
F.29 Fault: Flame loss Gas supply temporarily stopped, flue gas recirculation, incorrect earthing of
product, ignition transformer has spark failure
F.32 Fan frost protection function active: Fan
speed outside the tolerance values
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
F.33 Fan frost protection function active: Air
pressure switch fault
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,
hose removed from between the pressure monitor and silencer, air/flue pipe
blocked
F.49 eBUS fault: Voltage too low Short circuit on eBUS, eBUS overload or two power supplies with different
polarities on the eBUS
F.61 Fault: Gas valve control system Short circuit/short to earth in cable harness for the gas valve, gas valve
defective (coils shorted to earth), electronics defective
F.62 Fault: Gas valve switch-off control Delayed switch-off of gas valve, delayed extinguishing of flame signal, gas
valve leaking, electronics defective
F.63 Fault: EEPROM Electronics defective
F.64 Fault: Electronics/sensor/analogue-to-
digital converter
Flow or return NTC short circuited, electronics defective
F.65 Fault: Electronics temperature too high Electronics overheating due to external influences, electronics defective
F.67 Value sent back by ASIC is incorrect
(flame signal)
Implausible flame signal, electronics defective
F.68 Fault: Unstable flame (analogue input) Air in gas, gas flow pressure too low, incorrect air ratio, incorrect gas re-
strictor, ionisation flow interruption (cable, electrode)
F.70 Invalid product code (DSN) Display and PCB replaced at same time and Device Specific Number not
reset, wrong or missing output range coding resistance
F.71 Fault: Flow/return temperature sensor Flow temperature sensor signalling constant value: Flow temperature sensor
incorrectly positioned on supply pipe, flow temperature sensor defective
F.72 Fault: Deviation in the water pressure
sensor/return temperature sensor
Flow/return NTC temperature difference too great → flow and/or return tem-
perature sensor defective
F.73 Fault: Water pressure sensor not con-
nected or has short-circuited
Interruption/short circuit of water pressure sensor, interruption/short circuit
to GND in supply line to water pressure sensor or water pressure sensor
defective
F.74 Fault: Electrical problem in the water
pressure sensor
Line to water pressure sensor has a short circuit to 5 V/24 V or internal fault
in the water pressure sensor
F.75 Fault: Pressure sensor Pressure switch defective
F.76 The safety cut-out in the primary heat
exchanger is defective
Safety cut-out feedback does not match the gas valve feedback
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