Boiler Not Working? A Step-by-Step Troubleshooting Guide

Before calling a plumber, check these common boiler issues. Many lockouts and faults can be resolved in minutes without engineer attendance.

Check These First

Don't panic — the majority of boiler "faults" are caused by simple issues you can resolve yourself in a few minutes. Work through these checks before calling an engineer.

1. Check the Boiler Pressure

Look at the pressure gauge on the front of the boiler. It should read between 1 and 1.5 bar. Below 1 bar, the boiler will usually lock out with a low-pressure error code. See our guide on re-pressurising your boiler — it's a 5-minute job.

2. Check the Error Code

Modern boilers display an error or fault code when they lock out. Common codes include:

Worcester Bosch: A1 = low water pressure, E9 = overheating, H07 = fan fault
Vaillant: F22 = low pressure, F29 = ignition failure, F75 = pressure sensor
Baxi: E1 = low pressure, E119 = low water pressure

Search the code with your boiler model for the specific meaning.

3. Try a Boiler Reset

After fixing the underlying issue (e.g. re-pressurising), most boilers need a manual reset. Hold the reset button for 3–5 seconds. If the boiler fires and runs normally for several minutes before locking out again, call us — there's an underlying fault.

4. Check the Thermostat and Timer

Confirm the room thermostat is set above the current room temperature. Check the programmer/timer to ensure the heating is set to "on" — they can accidentally be knocked to "off".

5. Check for a Frozen Condensate Pipe

In freezing weather, the condensate pipe (a small plastic pipe that exits the boiler through an external wall) can freeze solid. The fix: pour warm (not boiling) water over the pipe where it exits the wall, then reset the boiler.

When to Call Us

Call us immediately if: you suspect a gas leak (smell of gas), there is any visible damage to the boiler, the boiler is making loud banging or crackling sounds, or you cannot resolve the fault after the above steps.