A boiler not working is usually caused by low pressure, a thermostat or power fault, a pilot light or ignition problem, or a frozen condensate pipe.
Why Is My Boiler Not Working?
When your boiler stops working, you can quickly lose heating or hot water. This is particularly frustrating during winter when you need your home to stay warm.
There are several possible causes. The boiler may have low pressure, a faulty thermostat, an ignition problem or a frozen condensate pipe.
I recommend starting with a few simple checks before arranging a repair. Here is my diagnostic checklist to help you identify the problem and understand when to call a heating engineer.
⚠️ Important: If you smell gas, leave the property, avoid operating electrical switches and call the National Gas Emergency Service on 0800 111 999 in Great Britain.
1. Check the Boiler Error Code
Look at the boiler display for an error code or warning light. This can help identify the fault, such as low pressure, ignition failure or overheating.
Check your boiler manual to understand what the code means. Make a note of it before contacting an engineer.
If the error keeps returning, arrange a professional inspection. Never remove the boiler casing or attempt internal repairs yourself.
2. Check the Boiler Pressure
Low boiler pressure is a common reason for a boiler to stop working. Most sealed heating systems operate at around 1 to 1.5 bar when cold, although you should follow your manufacturer's guidance.
- Below 1 bar: The pressure may be too low.
- Around 1 to 1.5 bar: This is a typical cold pressure range.
- Above 2.5 to 3 bar: The pressure may be too high.
If the pressure is low, follow your boiler manual to repressurise it or contact an engineer. If it keeps dropping, there may be a leak or another fault.
3. Check the Thermostat
Sometimes the boiler is working correctly, but the heating controls are not calling for heat. Check that:
- The thermostat is switched on.
- The target temperature is higher than the room temperature.
- The heating schedule is correct.
- The batteries work, if required.
- A wireless thermostat is connected to its receiver.
If the controls appear to be working but the heating stays off, the problem may involve the wiring, receiver or boiler.
4. Check the Power Supply
Your boiler needs electricity to operate, even if it uses gas for heating.
If the display is blank, check that the boiler's power switch is on. If you can safely identify the relevant circuit breaker, check whether it has tripped.
If the breaker trips again, do not keep resetting it. Contact a qualified electrician or heating engineer.
5. Check the Pilot Light
Some older boilers use a permanent pilot light. If it goes out, the boiler may stop producing heat. Modern boilers usually use electronic ignition instead.
If your boiler has a pilot light, follow the manufacturer's instructions before attempting to relight it.
If it will not stay lit or the boiler repeatedly fails to ignite, stop trying and arrange a repair from a Gas Safe registered engineer.
6. Look for a Frozen Condensate Pipe
A frozen condensate pipe can stop your boiler working in winter. It carries wastewater away from your boiler. Exposed sections can freeze in cold weather.
Check the manufacturer's instructions. If it is safe, use warm water to thaw the pipe. Never use boiling water, a naked flame or a blowtorch. If the boiler still does not work, contact a heating engineer.
7. Check the Gas Supply
If the boiler will not ignite, there may be a problem with the gas supply.
If it is safe and there is no smell of gas, check whether other gas appliances are working. If you use a prepayment meter, check that you have credit.
Never attempt to repair gas pipework or internal boiler components yourself. Any gas appliance work must be carried out by a Gas Safe registered engineer.
8. Look for Leaks or Unusual Noises
Water around the boiler or persistent banging, whistling or gurgling can indicate a fault.
Check accessible pipes and radiators for visible leaks, but do not remove the boiler casing.
If you find a leak, keep water away from electrical equipment and isolate the water supply if you can do so safely. Arrange a professional inspection if the boiler is leaking, making unusual noises or repeatedly losing pressure.
9. Should You Reset the Boiler?
Some boilers can be reset after a temporary fault. Check your manual and follow the manufacturer's instructions.
If the same error returns or the boiler repeatedly locks out, stop resetting it. A reset may clear a warning temporarily, but it will not fix the underlying problem.
When Should I Call a Heating Engineer?
I recommend arranging a repair if your boiler continues to show an error code, loses pressure repeatedly, leaks water or fails to provide heating or hot water after these checks.
I understand how disruptive a broken boiler can be, especially during winter. If your boiler is still not working, contact us about our boiler repair service for help across South London and Surrey.
Frequently Asked Questions
Why is my boiler not working but the hot water is on?
The fault may affect the heating controls, circulation or a component such as the diverter valve. An engineer can identify the cause.
Can low pressure stop my boiler working?
Yes. Many boilers will stop operating if the pressure falls below the required level. Repeated pressure loss needs investigation.
Why does my boiler stop working in winter?
Cold weather can freeze condensate pipes, while increased heating demand may expose existing faults.
Is it safe to keep resetting my boiler?
No. If the same fault keeps returning, stop resetting it and arrange a professional inspection.
Boiler Not Working in South London?
R.W. Miller repairs boilers across South London and Surrey. Call Reion on 07375 813996, get in touch or book a boiler repair. We also cover boiler repairs in Wandsworth and Lambeth.
