Boiler Keeps Cutting Out — What To Do

Quick answer: A boiler that keeps cutting out is usually caused by low water pressure, overheating, a faulty thermostat, or a blocked condensate pipe. Some causes you can fix yourself — others need a Gas Safe engineer.

Common Reasons Your Boiler Keeps Cutting Out

1. Low Water Pressure

If the pressure drops below around 0.5 bar, most boilers will lock out as a safety measure. Check your pressure gauge — if it's in the red or below 1 bar, try re-pressurising the boiler.

Can fix yourself

2. Overheating

If the boiler gets too hot, a safety thermostat (overheat stat) will shut it down. This is often caused by a faulty pump not circulating water, a blocked heat exchanger, or too many radiator valves closed off.

Needs an engineer

3. Frozen Condensate Pipe

In winter, the plastic condensate pipe that runs outside can freeze, causing the boiler to lock out. You can often thaw it yourself with warm (not boiling) water poured over the pipe.

Can fix yourself

4. Thermostat or Timer Issues

A faulty room thermostat or programmer can cause the boiler to cycle on and off incorrectly. Check your thermostat settings and batteries first. If the problem persists, the thermostat may need replacing.

Check first, then call

5. Flame or Ignition Failure

If the boiler fires up but the flame goes out immediately, it could be a faulty flame sensor, blocked burner, or gas supply issue. This always requires a Gas Safe engineer — never attempt to fix gas components yourself.

Needs an engineer

What to Try First

Check the pressure gauge — top up if below 1 bar
Check for a fault/error code on the boiler display and look it up in your manual
Check the thermostat settings and replace batteries if needed
Check if the condensate pipe is frozen (in cold weather)
Press the reset button once and wait to see if it fires up successfully

Don't Keep Resetting

Pressing reset more than once or twice is not a fix — it's masking the problem. If your boiler keeps cutting out after a reset, call a Gas Safe engineer. Repeatedly forcing a faulty boiler to run can cause further damage or create a safety hazard.