Select a fault code
The boiler has failed to ignite. Low gas pressure or a faulty electrode are common causes.
Pressure has dropped below 0.5 bar. This is the most common Vaillant fault.
The flow temperature is increasing too rapidly, indicating circulation problems.
The ionisation electrode is not correctly detecting the flame.
The boiler tried to ignite but no flame was detected.
The flame went out during normal operation.
The fan is not running at the correct speed for safe combustion.
Gas pressure at the boiler is too low.
The gas valve relay has failed. The boiler cannot safely control gas.
A serious fault in the gas valve safety circuit.
Internal memory fault on the PCB.
The water pressure sensor has failed.
The pressure sensor detected no change when the pump activated, suggesting a pump or sensor fault.
The condensate drain is blocked or the condensate pump has failed.
Protect against future repair bills
Boiler cover means no surprise costs when things go wrong
Boiler & heating cover with no call-out fees
24/7 call-out, 4-hour emergency response
Nationwide network of engineers
Prices shown are indicative — actual cost depends on your boiler age and policy type.
Compare repair costs →📞 Vaillant Direct Support
Phone numbers are provided in good faith — always verify on the manufacturer's official website. PlumbingAdvice.co.uk is not affiliated with any boiler manufacturer.