Vaillant Boiler Error & Fault Codes

Vaillant Boiler guide by THS Plumbing & Heating Northampton

Most popular Vaillant Boiler Faults.

The F75 fault is typically the most popular vaillant failure and the fault is the water pressure sensor. If you have this fault, you'll need a new pressure sensor, get a quote for this repair or call us to have this fixed by one of our gas boiler engineers.

Fault F28 and F29 are common in winter due to a Frozen condensate pipe.

F28 and F29 vaillant faults are Frozen condensate pipe

If you need help or can't do this yourself, book one of our engineers who will happily come and do this for you.

NTC = Negative Temperature Coefficient
PCB = Printed Circuit Board

Vaillant ecoTEC Pro & ecoTEC Plus Fault/Error Codes.

Fault/Error Code Possible Cause
F00/F0 Heating Flow Temperature Sensor interruption or Heating Flow NTC Thermistor fault.
F01/F1 Return temperature sensor interruption NTC (Negative Temperature Coefficient) plug not plugged in or has come loose.
F10 Flow Negative Temperature Coefficient short circuit - NTC defective, short circuit in cable harness.
F11 Return Negative Temperature Coefficient short circuit - NTC defective, short circuit in cable harness.
F20 Safety switch-off - Temperature limiter Incorrect earth connection between cable harness and boiler. - Loose connection?
F22 Safety switch-off - Low water pressure, No water pressure, or water pressure is too low in the boiler. - Cable to the pump or water pressure sensor loose.
F23 Safety switch-off - Temperature difference. Pump blocked or insufficient pump output. Air in boiler. Temperature too great.
F24 Safety switch-off - Temperature difference. Pump blocked or poor pump performance. Air in boiler. Temperature is rising to fast.
F25 Safety switch-off - Temperature difference. Break in the plug connection for optional flue gas safety thermostat. Temperature too high.
F26 Fault - Gas valve without function or Gas valve stepper motor not connected. Plug on the PCB not plugged in correctly.
F27 Safety switch-off - Flame simulation - Moisture on the electronics. Flame monitor defective. Gas solenoid valve leaking.
F28 Strat-up failure - Ignition unsuccessful. Air in gas or gas flow pressure too low. Condensate pipe blocked. Fault on the gas valve or plug on PCB incorrectly plugged in.
F29 Operation failure - Re-ignition unsuccessful. Gas supply stopped or faulty earthing of boiler. Condensate pipe blocked. Transformer has spark failure.
F32 Fan fault - Plug at fan not correctly plugged in or Fan blocked. Sensor defective. Plug on PCB not correctly plugged in.
F49 eBUS fault - Short circuit on eBUS. What is eBUS? - eBUS is a communication protocol used to manage your Vaillant boiler.
F61 Gas valve regulation - Short circuit/short to earth. Book an engineer.
F62 Gas valve switch-off - Delayed shutdown of gas valve. Gas valve leaking or Electronics defective.
F63 EEPROM error - Electrically Erasable Programmable Read-Only Memory error. Electronics defective.
F64 Electronics or NTC fault - Book an engineer.
F65 Electronics overheating - Temperature fault. Electronics defective.
F67 Electronics or flame fault - Implausible flame signal or Electronics defective.
F68 Unstable flame - Air in gas, gas flow pressure too low, wrong air ratio. Book a Vaillant boiler service.
F70 Invalid DSN - Invalid device specific number.
F71 Fault flow temperature sensor - Flow temperature sensor positioned incorrectly at supply pipe (CHECK) or Flow temperature sensor defective (New Sensor).
F72 Flow/return NTC fault - Negative Temperature Coefficient temperature difference too great or sensor defective. (New Sensor).
F73 Water pressure sensor - Sensor signal in the wrong range - too low. Short circuit of water pressure sensor or water pressure sensor defective. (New Sensor).
F74 Water pressure sensor - Sensor signal outside correct range - too high. Short-circuited at 5 V/24 or internal fault in water pressure sensor. Water pressure sensor defective. (New Sensor).
F75 Water pressure sensor - No pressure detection when starting pump. Water pressure sensor defective. (New Sensor). Check adjustable bypass.
F76 Overheating - Protection on primary heat exchanger has responded. Primary heat exchanger defective. Book a Vaillant boiler repair
F77 No response from flue - Condensate pump fault or condensate pump defective.
F78 Interruption to DHW - Domestic hot water system outlet sensor at external controller UK link box is connected.
F83 Flow/return temperature sensor - Temperature change fault. When the burner starts, the temperature change registered non-existent or too small or not enough water in the boiler.
F84 Flow/return temperature sensor - Temperature difference implausible. Error with flow/return temperature sensor temperature changing error.
F85 Flow/return temperature sensor - Error with flow and return temperature, sensor incorrectly fitted . Fitted to the same pipe or wrong pipe.
F92 Coding resistor fault - he coding resistor on the PCB does not match. Check and enter the correct gas family.
F93 Gas group fault - Wrong gas restrictor or recirculation or wrong gas group. Internal pressure measuring point in venturi blocked. Do not use lubricant on O-ring.

Understanding the Vaillant Fault/Error Codes.

Some Vaillant fault and error messages are much less serious then other fault and error messages, and like the F28 and F29 codes, they mean that there is not enough gas (or the gas has stopped) getting into the boiler, which could happen when you have run out of gas on a prepaid meter or that the condensate pipe is blocked and would need unblocking.

If the worst comes to the worst and your Vaillant boiler needs a replacement part. Vaillant Boilers are design in the way that component replacement is easy and could be performed quickly.

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