Your boiler won't fire up or start. Here are some quick checks you can do:
DIY Checks You Can Do
Turn off the boiler
Switch it off immediately to prevent further damage.
Check where it's leaking
Is water coming from the bottom, pipes, or pressure relief valve? The location helps identify the problem.
Check boiler pressure
If the pressure gauge shows above 2.5–3 bar, the pressure is too high.
Look for obvious damage
Check for corroded pipes, loose connections, or damaged seals around the boiler.
Put towels down
Protect your floor and catch dripping water.
Still Won’t Fire Up?
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We're Advanced Heating and Plumbing, covering North London, West London, Watford, Herts and Middx. We can diagnose why your boiler won't start and fix it.
Call 0800 328 0449 nowCommon Reasons Why Boilers Won’t Fire Up
No Power Supply
If your boiler has no power or the display is blank, check:
Power switch on the boiler (often accidentally turned off)
Fuse in the fused spur near the boiler
Circuit breaker in the consumer unit (fuse box)
Timer settings
Fix: Reset the fuse or circuit breaker. If it trips again immediately, there’s an electrical fault that needs an engineer.
Low System Pressure
Most boilers won’t fire if pressure is too low.
Check: Pressure gauge should read 1–1.5 bar when cold.
Fix: Repressurise using the filling loop. If pressure drops again quickly, you may have a leak.
Thermostat Issues
Check: Heating mode on, temperature set higher than room level, replace batteries if wireless, and ensure it’s not in direct sunlight.
Fix: Adjust settings or replace batteries. If it still doesn’t respond, the thermostat may need replacing.
Frozen Condensate Pipe
A very common issue in cold weather. The condensate pipe can freeze, shutting the boiler down.
Check: Look for the small white plastic pipe outside the house.
Signs: Gurgling noises, boiler tries to fire but shuts down, or error codes appear.
Fix: Pour warm (not boiling) water over the external pipe to thaw it. Once thawed, reset the boiler.
Air in the System
Air trapped inside can prevent ignition.
Signs: Clicking or firing sounds but no ignition.
Fix: Bleed radiators and the boiler to release trapped air.
Faulty Ignition
The ignition system or electrode may have failed.
Signs: Boiler goes through its start-up cycle but doesn’t ignite.
Fix: Requires an engineer. Ignition leads, electrodes, or the gas valve may need replacing.
Gas Supply Issues
No gas may be reaching the boiler.
Check:
Are other gas appliances (like your cooker) working?
Is your gas meter displaying correctly?
Is the gas isolation valve near the boiler open?
Fix: If there’s no gas to the property, contact your gas supplier. If the valve is closed, open it carefully.
Boiler Lockout
If the boiler detects a fault, it locks out for safety.
Signs: Error codes or red flashing lights.
Fix: Try resetting using the reset button. If it locks out again, call an engineer.
When to Call an Engineer
After basic checks: If power, pressure, and thermostat are fine but it still won’t fire.
Error codes: Persistent codes need professional diagnosis.
Repeated lockouts: Resets don’t hold.
Won’t stay on: Fires up briefly then shuts down.
No gas: Other gas appliances work but boiler doesn’t.
Strange noises: Banging, grinding, or loud clicking.
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