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Heatsy Full List of Vaillant Fault Codes

May 27, 2021

We’ve put together a full list of Vaillant fault codes for Vaillant TurboMax through to Vaillant Ecotec boilers.

There’s a brief description of the probable causes, if you’d like a more in-depth breakdown have a look at our individual articles for some of Vaillant’s more common fault codes including Vaillant F61 or Vaillant F22 and Vaillant F75 fault codes.

Remember most of the work needed to diagnose the exact cause of your Vaillant boiler fault safely and accurately will need to be carried out by a competent Gas Safe registered boiler repair engineer.

This article is just meant as a guide, if you have a Vaillant F22 fault you could check a few external factors like air in your radiators or low water pressure but, anything involving gas or the need to remove the boiler casing will require a local GasSafe boiler repair engineer to attend.

Vaillant Fault Code Meaning Cause Explanation
F.00 Flow NTC open circuit NTC broken, cable broken, bad connections Flow sensor or wiring harness have failed.
F.01 Return NTC open circuit NTC broken, cable broken, bad connections Return sensor or wiring harness have failed.
F.02 DHW NTC open circuit NTC loose, defective, bad connections DHW sensor or wiring harness have failed.
F.10 Flow NTC short circuit NTC defective NTC defective or harness earthing failed.
F.11 Return NTC short circuit NTC defective NTC defective or harness earthing failed.
F.13 Tank NTC short circuit NTC defective NTC defective or harness earthing failed.
F.20 Safety temperature limiter by NTC activated Flow-NTC not correctly thermal-connected or defective; appliance does not shutdown. The flow temp. Has reached above 97 degrees. Possible, air, pump, sludge. Blocked heat ex., faulty NTC.
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. Water pressure sensor defective, cable to pump or water sensor defective, pump blocked or defective, pump output too low.
F.23 Water shortage Temperature difference between flow and return too large. Low water pressure, faulty pump, air, blocked system, faulty NTC.
F.24 Water shortage Temperature rise too quick. Low water pressure, faulty pump, air, blocked system, faulty NTC.
F.27 Incorrect sensing of flame Flame detector defective. Boiler has detected a flame when the boiler should be off. Possible flame rec prob, earthing, PCB.
F.28 Appliance does not start 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.

The boiler has attempted to ignite 3 - 5 times but failed. Check for gas at another outlet i.e., cooker, possible gas valve, low gas pressure, no gas, harness, PCB, plug, valve settings.
F.29 Flame goes off during ignition Gas supply temporarily stopped, faulty earthing of appliance. The boiler has detected a flame, but the flame has gone out immediately. Check low gas pressure, faulty valve, blocked flue, blocked burner, flame rec, poor earth, PCB.
F.32 Fan speed variation Fan blocked, plug not inserted correctly on fan, hall sensor defective, fault in cable harness, electronics defective. 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. Short circuit on eBUS, overload on eBUS or two power sources on eBUS with different polarity.
F.61 Gas Valve defective Short circuit/earth (ground) leak in cable harness to gas valves, gas. The gas valve hasn’t been powered to open- check PCB, polarity, earth, harness, gas valve, coils.
F.62 Gas valve shut off delay Gas valve leaking, electronics defective. The gas valve hasn’t closed immediately. Check valve, harness, PCB, earth, mini tightness test.
F.63 EEPROM Error - electronics. PCB, polarity.
F.64 Electronics/NTC fault Short-circuit in flow or return NTC or electronics defective. Polarity, harness, NTC, PCB.
F.65 Electronics temperature too high Electronics too hot due to external effect, electronics defective. PCB, Polarity, harness, NTC, G10 door seal.
F.70 No valid DSN in display and/or mainboard Spare part failure display and mainboard interchanged at same time and device specific number not adjusted. Usually occurs when a new PCB has been installed and the correct DSN (device specific number) has not been set.
F.71 Flow NTC reports constant value (stuck at) Flow NTC is defective. Flow NTC is defective.
F.72 Flow and/or return NTC fault Flow and/or return NTC is defective (tolerances too big). Flow and/or return NTC is defective (tolerances too big).
F.73 Water pressure sensor signal out of range (too low) Cable to water pressure sensor is broken or has a short-circuit at 0V or water pressure sensor defective. Loose connection, faulty sensor, blocked sensor, harness, poor earth.
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. Loose connection, faulty sensor, blocked sensor, harness, poor earth.
F.75 No pressure rise was detected on turning on the pump Water pressure sensor or/and pump defective. Too little water in appliance; check adjustable by-pass; connect external expansion vessel to return. The sensor has not detected a rise in pressure when pump starts, blocked sensor, faulty sensor, low water pressure, poor or faulty pump, PCB, air, blocked system, blocked filter.
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. Loose connection on harness, blocked hex, pump, air - new heat exchanger will be needed.
F.77 condensate pump or feedback of accessory blocks heating Condensate pump defective or flume flap feedback triggered. Condensate backed up and not drained away, check pump, power, discharge point i.e., sink waste for blocks.
F.78 wrong configuration with accessory link box VR65 connected to combination boiler con no communication to mainboard connection error display mainboard. Incorrect wiring, faulty, VR65, harness.

If you’re experiencing any of the Vaillant fault codes listed above with your Vaillant boiler, please give us a call on 0207 099 9035 or visit www.heatsy.co.uk

We are proud to be recognised as Vaillant advance installers and have a wealth of knowledge repairing, maintaining, and installing Vaillant boilers of all ages and models, from the Vaillant ThermoCompact of the late 80s to the Vaillant ecoTec plus range of the present day.

If your Vaillant boiler has a fault code, we have the skill to repair it.

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