A boiler that won’t fire up — no ignition, no heating, no hot water — is one of the most common call-outs we get, especially in colder months. Often the cause is something simple you can check yourself before calling an engineer. This guide covers why a boiler won’t fire up and how to fix it safely.
Quick checks before you call anyone
- Check the thermostat. Make sure it’s set above the current room temperature and, if it’s battery-powered, that the batteries aren’t flat.
- Check the boiler pressure. Most combi boilers need 1 to 1.5 bar when cold. If the gauge is below 1, low pressure can stop the boiler firing — top it up using the filling loop, or see our guide on boiler pressure.
- Check the power and fuse. A tripped switch in the fuse box can cut power to the boiler. Reset it and see if the boiler comes back on.
- Check your gas supply. Make sure other gas appliances (hob, other heating) are working. If you’re on a prepayment meter, check you have credit, and that the gas valve is open.
- Check the timer or programmer. Confirm the heating is actually scheduled to be on and the clock is set correctly.
- Look for a fault code. Most modern boilers show an error code on the display. Note it down — it tells the engineer exactly what’s wrong.
- Try one reset. If there’s a reset button and a fault code, press it once. If the boiler fires and then locks out again, stop and call an engineer rather than repeatedly resetting.
Common reasons a boiler won’t fire up
- Low boiler pressure: the most common and easily fixed cause.
- No gas supply: a supply issue, closed valve or empty prepayment meter.
- A frozen condensate pipe: in freezing weather the external condensate pipe can freeze and lock the boiler out. Thawing it with warm (not boiling) water often restores the boiler.
- A faulty thermostat: if it isn’t telling the boiler to fire, nothing happens.
- Ignition, fan, gas valve or PCB faults: internal faults that need a Gas Safe registered engineer.
When to call a Gas Safe engineer
Checking the pressure, thermostat, fuse and condensate pipe is safe to do yourself. Anything internal — ignition faults, the gas valve, the PCB, or a boiler that keeps locking out — must be handled by a Gas Safe registered engineer. If you’ve run the checks above and the boiler still won’t fire, it’s time to book a boiler repair. For a wider walkthrough of what to do when the heating stops, see our boiler breakdown guide, and if the boiler fires for heating but you have no hot water, see this guide.
Safety first: if you ever smell gas, don’t touch the boiler — turn off the gas at the meter, open windows, and call the National Gas Emergency line on 0800 111 999.
Frequently asked questions
Why won’t my boiler fire up but there’s power?
Power to the display doesn’t mean the boiler can fire. The usual culprits are low pressure, no gas, a frozen condensate pipe, or a thermostat not calling for heat. Check those first.
Can low pressure stop a boiler firing up?
Yes. If pressure drops below around 1 bar, many boilers lock out and won’t fire until it’s topped back up to 1–1.5 bar.
Should I keep pressing the reset button?
No. Try a reset once. If the boiler fires then locks out again, repeated resets can make things worse — call an engineer.
Boiler still won’t fire up? We can help
Our Gas Safe registered engineers provide fast boiler repairs and plumbing and heating services across West London, usually fixing the fault in a single visit. Call 020 3561 4415 or contact us for same-day help.