Symptom guide
What's wrong with my boiler?
Plain-English symptoms, then local installer introductions. Up to three firms can contact you about quotes.
Safety first
Smell gas?
Leave the property, avoid switches and call the National Gas Emergency Service on 0800 111 999.
Carbon monoxide alarm
If an alarm sounds or you suspect CO, get fresh air, call 999 or 111 and do not use the appliance until it is checked.
Major leak or flooding
Turn off the boiler and isolate the water supply if it is safe to do so. Keep electrics clear of water.
Do not open sealed panels
Only a Gas Safe registered engineer should remove a boiler casing or work on gas parts.
How to use this guide
Pick the symptom that sounds closest to what you are seeing. Note your boiler type and fuel if you know them, such as combi, system, regular, gas, LPG, oil or electric. Then open the quote form and we will introduce installers who can diagnose the problem on site.
Common symptoms
No heating
Radiators stay cold while the programmer is on. Often a controls, pump or valve issue, but a boiler fault is possible too. Note whether hot water still works.
No hot water
Common on combi boilers from a diverter valve, plate heat exchanger or low pressure fault. Cylinder systems may have a thermostat or immersion issue.
No heating and no hot water
Usually points to a total boiler lockout, no power, no gas, or very low pressure. Check the display, timer and pressure gauge first.
Locking out / fault code
Modern boilers show a fault code when they fail to light or overheat. Note the exact code and any pattern, such as after running hot water.
Strange noise
Banging, gurgling or whistling can mean air, sludge, scale on the heat exchanger or a failing pump. A recording helps an engineer narrow it down.
Low pressure
Pressure below roughly 1 bar often locks the boiler. A small top-up may fix it, but repeated pressure loss usually means a leak somewhere in the system.
Radiators uneven
Some hot, some cold, or hot at the top and cold at the bottom. Could be air, sludge, a stuck valve or an imbalance across the system.
Leaks
Water under the boiler, from a pipe or through the wall. Turn the boiler off and isolate water if safe. Photograph where the water is coming from.
Ignition or pilot light
Pilot keeps going out or ignition fails repeatedly. Could be a thermocouple, electrode, gas valve or flue issue. Do not try to relight it repeatedly.
Planning a replacement
Age, repair history and parts availability matter more than a fixed age limit. A site survey is the only way to size and price the right boiler.
What not to do
Do not open sealed boilers
Boiler casings and gas parts must only be opened by a qualified engineer.
Do not ignore CO alarms
Treat every carbon monoxide alarm as serious. Ventilate and seek professional help.
This page is not a verdict
It is a guide to help you describe the problem. Only a site survey can confirm what needs fixing or replacing.
Do not delay gas escapes
If you smell gas, call the National Gas Emergency Service on 0800 111 999 before arranging quotes.
Ready to find a local installer? Get up to three quotes.
BoilerMatch UK introduces homeowners to local heating installers and you decide who, if anyone, you hire. We are not the Gas Safe Register, we do not fit or repair boilers ourselves, and any quote, work or warranty is agreed directly between you and the installer.