Boiler fault codes
Vaillant Boiler Fault Codes Explained
Vaillant boilers show two kinds of code. An F code, such as F.22 or F.28, means the boiler has stopped because of a fault. An S code, such as S.03, is only a status message telling you what the boiler is doing. Find your F code below for what it means and what is safe to try.
How do I read a Vaillant boiler display?
On an ecoTEC plus or ecoTEC pro the code appears as a letter, a dot and two digits. Newer models also show a short text description next to it. If the boiler has locked out, the code stays on screen until the fault clears or you press reset.
S codes are not faults. S.03 means the boiler is lighting for heating, S.30 means the room thermostat is not calling for heat, and S.41 means system pressure is too high. On current ecoTEC plus models they appear in the Live monitor menu. If your boiler shows an S code and no heat, the controls are usually the place to look, not the boiler.
The pressure reading matters as much as the code. Vaillant's installation manual says the pressure figure flashes on current ecoTEC plus models once it falls below 0.8 bar, and the boiler stops with F.22 below 0.5 bar. Several of the codes below are triggered by low water, so check the gauge before anything else.
Which Vaillant codes can I deal with myself?
Vaillant's own advice is to try a reset, following your user manual, before calling anyone. Beyond that, the codes split roughly into three groups.
- Water and pressure: F22 low water pressure and F75 are the codes Vaillant says a competent householder can fix by topping up, if the gauge reads below 1 bar. F23 and F24 are circulation faults, often from low pressure or air. Check the gauge, but Vaillant’s advice for both is to call an installer.
- Ignition: F28 means the boiler failed to light and F29 means the flame went out and would not relight. Vaillant suggests checking the gas supply, prepayment meter credit and whether the condensate pipe outside has frozen.
- Engineer only: F20 overheat cut-out if it repeats, F32 fan fault, F61 and F62 gas valve faults, and F83 no temperature rise at start-up.
Press reset once, not repeatedly. A code that returns straight away is telling you the cause is still there. Nothing inside the casing is a householder check, and if you smell gas, open windows, turn the gas off at the meter if you safely can, avoid switches, then get out and call 0800 111 999 before anything else.
When a Vaillant code needs a visit
Call an engineer if the same code returns after one reset, if the code is in the engineer-only group above, or if the boiler bangs, hums or smells of burning before it locks out. The code narrows the search, but it does not replace testing: F.75, for example, can be the pump, the pressure sensor or air in the system.
Gas work is carried out by Gas Safe registered engineers. Our visit starts with the £60 call-out, and the repair price is agreed with you on site before any work starts. You can book through Vaillant boiler repair.
| Code | What it means | Can you clear it yourself? |
|---|---|---|
| F.20 | Overheat: the safety cut-out tripped at the flow or return | Yes, once; call if it returns |
| F.22 | Low water pressure; the boiler stops below 0.5 bar | Yes, once; call if it returns |
| F.23 | Flow and return temperature gap too big: poor circulation | No, call an engineer |
| F.24 | Temperature rising too fast: water not flowing properly | No, call an engineer |
| F.25 | Flue gas temperature too high, so the boiler shut off | No, call an engineer |
| F.27 | Flame signal detected while the burner is off | No, call an engineer |
| F.28 | The boiler failed to light at start-up | Yes, once; call if it returns |
| F.29 | Flame lost while running and the relight failed | Yes, once; call if it returns |
| F.32 | Fan fault: speed cannot be confirmed | No, call an engineer |
| F.61 | Fault in the circuit that drives the gas valve | No, call an engineer |
| F.62 | Flame took too long to go out after the gas valve closed | No, call an engineer |
| F.63 | Memory (EEPROM) fault on the control board | No, call an engineer |
| F.75 | No pressure rise detected when the pump starts | Yes, once; call if it returns |
| F.83 | Little or no temperature rise when the burner lights | No, call an engineer |
Vaillant codes explained
- F20The boiler's overheat protection has tripped: the water temperature at the flow or return sensor went over the safety limit, so the boiler closed the gas valve and shut itself off.
- F22The boiler has switched itself off because there is not enough water, or not enough water pressure, in the heating circuit. Vaillant calls it a safety switch-off for low water pressure.
- F23The gap between the flow temperature (water leaving the boiler) and the return temperature (water coming back) is too large, which tells the boiler that water is not circulating properly. It shuts down to protect the heat exchanger.
- F24The temperature inside the boiler rose faster than it should after the burner lit, which means water is not flowing through the heat exchanger properly. The boiler shuts down before it can overheat.
- F25A safety shut-off: the boiler has detected, or thinks it has detected, flue gas temperature that is too high, and has switched itself off.
- F28The boiler tried to light on start-up, never detected a flame, and locked itself out. Vaillant describes it as the flame signal not being detected during the ignition phase.
- F29The boiler was running, lost its flame, and the attempt to relight failed. Vaillant describes it as unsuccessful ignition following a flame loss during operation.
- F32A fan fault: the boiler cannot confirm its fan is running at the right speed, so it switches off rather than light the burner.
- F61F.61 means the boiler has found a fault in the circuit that drives its gas valve, so it has shut the gas off and locked out. The cause is in the valve, its wiring or the control board, all inside the casing.
- F62F.62 means that when the boiler told the gas valve to close, the flame took too long to go out. The boiler reads that as a gas valve that may not be shutting off cleanly, and locks out.
- F75F.75 means the boiler switched its pump on and the water pressure sensor did not register the small pressure rise it expects. Low pressure, trapped air, a failing pump or a faulty pressure sensor are the usual causes.
- F83F.83 means that when the burner lit, the flow or return temperature sensor registered little or no rise in temperature. The boiler reads that as water not moving through the heat exchanger properly, or a sensor reading wrongly, and shuts down.
Questions people ask
Where is the reset button on a Vaillant boiler?
It is on the control panel on the front. Depending on the model it is marked with a reset symbol or the word reset. Your user manual shows it for your model.
Why does my Vaillant show a code but still seem to work?
It is probably an S status code rather than an F fault code. S codes change as the boiler moves between lighting, heating and standby, and they need no action.