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Writer's pictureJeff Culkin

Combination Pro 24 Pro 28 Plus 824 Plus 831 Plus 837


Code, Meaning, Official Cause, Our Comments

F. 0 Flow–NTC open circuit NTC broken, NTC cable broken, Defective connection at NTC, Defective connection at electronics

F. 1 Return–NTC open circuit NTC broken, NTC cable broken, Defective connection at NTC, Defective connection at electronics

F.10 Flow NTC short circuit NTC defective, short circuit in cable harness, cable/casing shortcut

Check for leaks and water causing short circuit

F.11 Return NTC short circuit NTC defective, short circuit in cable harness, cable/casing shortcut

Check for leaks and water causing short circuit

F.13 Tank NTC short circuit NTC defective, short circuit in cable harness, cable/casing shortcut

Check for leaks and water causing short circuit

F.20 Safety temperature limiter by NTC activated Flow-NTC not correctly thermal-connected or defective; appliance does not shut down

F.22 Dry fire Too little water in the appliance, water pressure sensor defective, cable to pump or water sensor defective, pump blocked or defective, pump output too low

Too much air in system or low water pressure

F.23 Water shortage, temperature difference between flow and return NTC too large Pump blocked or defective, pump output too low, flow and return NTC interchanged

Pump failure, flow and return reversed, air lock, blocked pipe, air in heat exchanger, or top up system in sealed system.

F.24 Water shortage, temperature rise too quick Pump blocked, insufficient pump output, air in appliance, water pressure too low

Too much air in system or low water pressure, failed or failing pump.

F.25 Interruption in the compact thermal module cable harness Compact thermal module cable harness defective

F.27 Incorrect sensing of flame Flame detector defective (Also check Gas Valve, and gas supply)

F.28 Appliance does not start: Attempts to ignite during start failed Faults in the gas supply such as: - Gas meter or gas pressure detector defective - Air in gas - Gas flow pressure too low - Fire protection tap has disengaged Faults in the gas valve, wrong gas setting, igniter (ignition transformer, ignition cable, ignition plug) defective, ionisation current stopped (cable, electrode), faulty earthing in appliance, electronics defective

Check gas supply, check maintenance works by National Grid these can come as a surprise

F.29 Flame goes off during operation and subsequent ignition attempts failed Gas supply temporarily stopped, faulty earthing of appliance

Check gas supply, check maintenance works by National Grid these can come as a surprise

F.32 Fan speed variation Fan blocked, plug not inserted correctly on fan, hall sensor defective, fault in cable harness, electronics defective

F.49 eBUS undervoltage Short circuit on eBUS, overload on eBUS or two power sources on eBUS with different polarity

F.61 Gas–valve control defective Short circuit/earth (ground) leak in cable harness to gas valves, gas valve assembly defective (earth/ground leak from coils), electronic control system defective

F.62 Gas valve shutoff delay Gas valve leaking, electronics defective

F.63 EEPROM error Electronics defective F.64 Electronics/NTC fault Short-circuit in flow or return NTC or electronics defective

F.65 Electronics temperature too high Electronics too hot due to external effect, electronics defective

F.67 Flame detector input signal is outside the limits (0 or 5 V) Electronics defective F.70 No valid DSN in display and/or mainboard Spare part failure display and maiboard interchanged at same time and device specific number not adjusted F.71 Flow NTC reports constant value (stuck at) Flow NTC is defective

F.72 Flow and/or return NTC fault Flow and/or return NTC is defective (tolerances too big)

(two different thermo-stats to check, also check pump and circulation)

F.73 Water pressure sensor signal out of range (too low) Cable to water pressure sensor is broken or has a short-circuit at 0 V or water pressure sensor defective

F.74 Water pressure sensor signal out of range (too high) Cable to water pressure sensor has a short-circuit at 5 V / 24 V or internal fault in water pressure sensor

F.75 No pressure rise was detected on turning on the pump Water pressure sensor or/and pump defective Air in the heating system, quick bleeder defective Too little water in appliance; check adjustable by-pass; connect external expension vessel to return

see f75 page (coming soon) Google f75 kit

F.76 Overheating protection on primary heat exchanger triggered Cable or cable connection of fuse in the primary heat exchanger defective, or primary heat exchanger defective

Replacement stat is not necessarily available due to safety concerns following an F76 incident

F.77 condensate pump or feedback of accessorie blocks heating condensate pump defective or flume flap feedback triggered

F.78 wrong configuration with accessory link box VR65 connected to combination boiler (Plug ins anre not correct; Controls wiring fault control)


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