Boiler not working? 8 things to check before you call
If your boiler has stopped working, run these eight checks before you call anyone. The common causes are low pressure, no power, the thermostat, no gas, a frozen condensate pipe, a tripped switch, the timer settings or a fault code on the display. Several of these you can fix yourself in a few minutes. If none of them solve it, it needs a Gas Safe engineer.
Work through the list in order. Do not attempt anything that involves removing the boiler casing or touching gas components, that is engineer-only.
1. Check the pressure gauge
Look at the pressure dial or display. It should normally sit around 1 to 1.5 bar when the heating is off. If it has dropped below 1, the boiler may shut down for safety. Most boilers have a filling loop you can use to top it back up following the manufacturer’s instructions. A pressure that keeps dropping points to a leak and needs an engineer.
2. Check the power
Make sure the boiler is switched on at its fused spur or socket and that a switch has not been knocked off. Check the consumer unit for a tripped breaker. If a breaker trips again straight after resetting, stop and call an engineer, that is an electrical fault.
3. Check the thermostat
Check the room thermostat is set above the current room temperature and is calling for heat. If it is battery powered, replace the batteries, flat thermostat batteries are a surprisingly common cause of no heating.
4. Check the timer and programmer
A power cut or the clocks changing can reset a programmer to off or to the wrong schedule. Confirm the time and the heating schedule are correct, and try a manual boost to rule the timer in or out.
5. Check you have gas
Check other gas appliances, like a hob, are working. If nothing gas is working, the issue may be your gas supply or the prepayment meter, not the boiler. If you smell gas, do not check anything, leave and call the emergency gas line on 0800 111 999.
6. Check the condensate pipe (in cold weather)
In freezing weather the condensate pipe, the plastic pipe running outside, can freeze and shut the boiler down, often with a fault code. Gently warming it with a hot water bottle or a jug of warm (not boiling) water along the external pipe can clear it. Never use boiling water.
7. Read the fault code
Most modern boilers show a fault or error code on the display. Note it down. Some codes clear with a single reset using the boiler’s reset button (press once, do not keep resetting). The code also tells the engineer exactly what to bring.
8. Try one reset
If there is a reset button, press it once and wait. If the boiler fires and stays on, the fault may have been a one-off lockout. If it locks out again, stop resetting, repeated resets can make things worse, and book a repair.
When to stop and call
Call a Gas Safe engineer if: pressure keeps dropping, a breaker keeps tripping, there is a leak, you see a yellow rather than blue flame, you smell gas, or the fault returns after a reset. A yellow flame or a gas smell is urgent, turn the boiler off and ventilate.
If the checks have not fixed it, book a same-day boiler repair and an engineer will diagnose it properly. If your heating works but you have no hot water, see our guide on no hot water but heating still working, that is usually a specific part.