Complete guide to Vaillant ecoTEC, ecoFIT, and turboTEC boiler fault codes with troubleshooting advice and DIY fixes
When your Vaillant boiler displays a fault code like F.28 on the screen, it's telling you something needs attention. Use our guide below to identify your error code and find out what it means.
Tip: Note down the exact code shown on your display - Vaillant codes start with 'F' followed by numbers (e.g., F22, F28, F75).
| Code | Meaning | Quick Fix | If That Doesn't Work | DIY? |
|---|---|---|---|---|
| F22 | Low water pressure - the system pressure has dropped below safe operating level | Check the pressure gauge on your boiler. If below 1 bar, use the filling loop to top up to 1.0-1.5 bar. Reset the boiler. | Likely a leak in the system or faulty expansion vessel. Call an engineer. | Yes |
| F75 | Pump/pressure sensor fault - no pressure rise detected when pump starts | Check system pressure and top up if needed. Try resetting the boiler. | Usually a stuck pump or faulty pressure sensor. Engineer required. | No |
| F24 | Temperature rising too quickly - insufficient water circulation | Check radiators are on, bleed any airlocks. Verify pressure is adequate. | Pump failure, blockage, or heat exchanger issue. Call an engineer. | Partial |
| F25 | Flue overheat - exhaust gas safety cutout activated | Wait for boiler to cool and reset. Check flue is not blocked. | Flue thermistor or internal fault. Engineer needed. | No |
| Code | Meaning | Quick Fix | If That Doesn't Work | DIY? |
|---|---|---|---|---|
| F28 | Ignition failure - boiler failed to ignite after multiple attempts | Winter: Check if condensate pipe is frozen - pour warm (not boiling) water over external pipe. Otherwise: Check gas supply is on, prepay meter has credit. | Gas valve, ignition electrodes, or PCB fault. Gas Safe engineer required. | Partial |
| F29 | Flame loss during operation - flame extinguished unexpectedly | Check gas supply. In winter, thaw condensate pipe. Reset boiler. | Intermittent gas supply, blocked flue, or faulty flame sensor. | Partial |
| F27 | Flame sensing fault - flame detected when there shouldn't be one | Reset boiler and monitor. Do not repeatedly reset. | Gas valve not closing properly - call Gas Safe engineer immediately. | No |
| F32 | Fan speed fault - fan not reaching required speed | Reset the boiler. Check nothing is blocking the flue outside. | Worn fan motor or wiring fault. Engineer required. | No |
| F33 | Air pressure switch fault - safety interlock not activating | Reset boiler. Ensure flue terminal is clear of debris. | Faulty pressure switch or fan. Gas Safe engineer needed. | No |
| Code | Meaning | Quick Fix | If That Doesn't Work | DIY? |
|---|---|---|---|---|
| F83 | Flow/return temperature sensor fault - abnormal temperature reading | Check system has adequate water. Reset boiler. | Faulty NTC sensor or air in system. Engineer required. | No |
| F10 | Flow temperature sensor short circuit | Reset the boiler. | Sensor or wiring fault. Requires engineer. | No |
| F11 | Return temperature sensor short circuit | Reset the boiler. | Sensor or wiring fault. Requires engineer. | No |
| F12 | Flow temperature sensor open circuit | Reset the boiler. | Disconnected or faulty sensor. Engineer needed. | No |
| F13 | Return temperature sensor open circuit | Reset the boiler. | Disconnected or faulty sensor. Engineer needed. | No |
| F20 | Overheat protection activated - boiler too hot | Let boiler cool down. Ensure radiators are open. Bleed air from system. | Pump failure, blockage, or faulty overheat stat. | Partial |
| Code | Meaning | Quick Fix | If That Doesn't Work | DIY? |
|---|---|---|---|---|
| F61 | Gas valve control fault - valve not responding correctly | Reset boiler. Do not repeatedly reset if fault returns. | Gas valve or PCB fault. Gas Safe engineer essential. | No |
| F62 | Gas valve shutoff delay fault | Reset boiler once. | Gas valve sticking or PCB issue. Engineer required. | No |
| F63 | EEPROM fault - internal memory error | Reset boiler. | PCB replacement likely needed. | No |
| F64 | Electronics/sensor fault - general electronic error | Reset boiler. | PCB or sensor wiring issue. Engineer required. | No |
| F65 | Electronics temperature fault - PCB overheating | Let boiler cool, ensure ventilation around boiler is adequate. | Ventilation issue or faulty PCB. Engineer needed. | No |
| F70 | Invalid display replacement - wrong display fitted | N/A - this occurs after incorrect part fitting. | Original display or correct replacement needed. | No |
| F71 | Flow temperature sensor fault - incorrect readings | Reset boiler. | Sensor replacement required. | No |
| F72 | Flow/return temperature discrepancy too great | Check system circulation. Bleed radiators. | Sensor fault or circulation problem. Engineer needed. | Partial |
Most Vaillant boilers can be reset by pressing the reset button (flame/power symbol) for 3-5 seconds. The exact method varies by model:
Important: If the boiler locks out again immediately after resetting, do NOT keep resetting. This can damage components. Call a Gas Safe engineer instead.
If your boiler fault requires professional attention, our Gas Safe registered engineers are here to help. We service all Vaillant models across Harrow, London and surrounding areas.