Common boiler problems
Most boiler problems come down to a few causes: low pressure, a frozen pipe, a setting that's changed or a worn part. Some you can check safely yourself. Others need a Gas Safe engineer. Find your problem below.
Updated 02/11/2026 · Express Contractors
Safety first
Smell gas? Call the National Gas Emergency line on 0800 111 999 straight away. Open doors and windows. Don't use light switches or anything that could spark. Turn the gas off at the meter if you can do it safely, then go outside.
Headaches, dizziness, sickness or a lazy yellow flame? These can be signs of carbon monoxide (CO), a poison gas you can't see or smell. Turn the boiler off, open windows, get everyone outside and call 0800 111 999. See a doctor if anyone feels unwell. Our carbon monoxide advice has more.
Never open the boiler case. Only a Gas Safe registered engineer should take the cover off a gas boiler. The checks in our guides are all ones you can do from the outside.
Water leaking near the boiler? Keep it away from sockets and the boiler's electrics. If water is pouring out, turn off the stopcock and see our emergency plumber page.
Check these first
These quick checks sort out a lot of problems. None of them need you to open the boiler.
- Power. Is the switch next to the boiler on? Has anything tripped at the fuse box?
- Gas. If your gas hob lights, the gas supply is fine. If you have a prepayment meter, check it has credit.
- Pressure. With the heating off, the gauge should usually read about 1 to 1.5 bar.
- Thermostat and timer. Turn the thermostat up a few degrees. Check the timer and its clock, especially after a power cut.
- Frozen pipe. In freezing weather, check the small plastic pipe outside. See our frozen condensate pipe guide.
- Reset once. If the boiler has a reset button, try it once. If it keeps cutting out, call an engineer.
Our boiler problem guides
Frozen condensate pipe
Your boiler stops on a freezing day. The small plastic pipe that drains it has iced up. You can often thaw it with warm water.
Boiler losing pressure
The gauge keeps dropping below 1 bar. How to top it up, and why it keeps happening.
Heating works but no hot water
Radiators hot but taps cold, or the other way round. Checks to try, and what a diverter valve does.
Cold radiators
Cold at the top, cold at the bottom, or cold all over. What each one means, and how to bleed a radiator.
Other common boiler problems
Here's a short note on each of these. Where we've written a full guide, the note links to it.
Cold radiators
A radiator cold at the top usually has air trapped in it, and bleeding it should help. Check the boiler pressure afterwards. A radiator cold at the bottom often has sludge inside. That may need a power flush, a deep clean of the pipes and radiators. Our plumber page explains it. For more, read our guide to cold radiators.
Boiler leaking water
Put a bowl or towel under the drip and keep water away from the electrics. A leak from inside the boiler needs a Gas Safe engineer. A drip from the small copper pipe outside can mean the pressure is too high. See boiler repair.
Boiler won't turn on, or keeps turning off
Start with the checks above. If it still won't fire up, or it keeps locking out, a part may have failed. Write down any fault code and call us for a boiler repair.
Noisy boiler
Banging, gurgling or a rumble like a kettle can mean air, sludge or limescale in the system. A gurgle on a freezing day can be a frozen condensate pipe. Other noises need an engineer to look. See boiler repair.
Fault codes
Each make uses its own codes, so check your boiler manual. Write down the code and the boiler model before you call. The code is only a starting point. An engineer first runs a thorough check of the boiler. That finds the fault and the parts it needs.
When to call a Gas Safe engineer
Call an engineer if:
- the simple checks haven't helped
- the boiler keeps locking out after a reset
- water is leaking from the boiler itself
- you need to top up the pressure often
- you smell burning, or see soot or black marks round the boiler
Only a Gas Safe registered engineer should open a gas boiler. By law, paid gas work must be done by a Gas Safe registered engineer. We repair all makes. See our boiler repair page for the faults we fix.
How to prevent boiler problems
A yearly boiler service is the best way to stop many faults. The engineer checks the boiler is safe, cleans key parts and spots wear early. Most makers also ask for a yearly service to keep the warranty valid.
If your boiler is old and keeps breaking down, a repair may not be the best value. We'll tell you honestly if a new boiler makes more sense.
Common questions
What are the most common boiler problems?
Low pressure, a frozen condensate pipe in winter, leaks, no hot water, cold radiators, strange noises and a boiler that keeps turning off. Many are caused by a worn part, and some are easy to check yourself first.
Can I fix my boiler myself?
You can do simple checks from the outside, like topping up the pressure, checking the thermostat and timer, resetting the boiler once and thawing a frozen condensate pipe. Never open the boiler case. Only a Gas Safe registered engineer should work on the inside of a gas boiler.
Is it safe to keep resetting my boiler?
Resetting it once is fine. If it keeps locking out, the boiler is shutting down for a reason. Resetting it again and again will not fix that, so call a Gas Safe engineer.
Boiler still not working?
Call us to book a boiler repair with a Gas Safe registered engineer. We repair all makes, and we're open 24/7.