Before you book an engineer, run these six checks. More often than you'd think, a dead boiler is a tripped switch, a flat battery, or a pressure gauge in the red - all things you can sort in minutes.
Never open the boiler casing or touch internal parts. These checks are all external and safe. Anything beyond them is a job for a Gas Safe engineer.
6 Checks Before You Call
Is the boiler's switch and fused spur on? Has the fuse board tripped? No display usually means no power.
Note any code or flashing light on the display - it tells the engineer exactly what's wrong.
The gauge should sit around 1-1.5 bar. Below 1, low pressure may be the entire problem.
Use the filling loop to bring pressure back to 1.5 bar - your manual shows how. Many boilers restart after this.
Turn it well above room temperature and check for fresh batteries. A dead thermostat won't fire the boiler.
Hold the reset button for a few seconds. One reset is fine; if it locks out repeatedly, stop and call.
What the Common Fault Codes Mean
- Low pressure code
- Follow the manufacturer instructions only if you can identify the external filling controls. Otherwise leave it to an engineer.
- Ignition / flame fault
- The boiler isn't lighting. Worth one reset, but if it repeats it needs an engineer.
- Frozen condensate
- Common in cold snaps - a frozen outlet pipe. Thawing it gently often gets you going again.
Thaw a Frozen Condensate Pipe
It's the white plastic pipe running outside, often to a drain. A blockage here is usually ice.
Pour warm - not boiling - water over the frozen section, or hold a covered hot water bottle against it.
Once the ice clears, reset the boiler. It should fire up normally.
Call an Engineer Now If…
- You smell gas - leave the house, open doors, and call the gas emergency line on 0800 111 999 in Great Britain (0800 002 001 in Northern Ireland; for LPG, contact your supplier)
- There's water leaking from the boiler
- The boiler locks out again straight after a reset
- The flame is yellow or orange instead of crisp blue
Stop It Happening Again
- Book an annual service - it catches faults before winter
- Insulate the outside condensate pipe to prevent freezing
- Keep an eye on the pressure gauge through the year
- Bleed your radiators each autumn so the system runs efficiently
Know Your System
The kind of boiler you have changes what can go wrong and how it's fixed. It helps to know which you've got before you call.
- Combi boiler
- One wall-mounted unit, no tanks. Heats water on demand. Most modern homes have one; pressure and ignition faults are common.
- System boiler
- Works with a hot water cylinder but no loft tank. Pump and diverter faults show up here.
- Conventional (heat-only)
- Older setup with a cylinder and a loft tank. More components, so more potential points of failure.
What an Engineer Checks That You Can't
Once the safe, external checks are done, the rest is for a Gas Safe engineer - these are internal, pressurised or gas components that are genuinely unsafe to touch.
- The PCB (circuit board) and wiring inside the casing
- Gas pressure and the combustion / flue readings
- The pump, diverter valve and heat exchanger
- Whether a cold radiator is the boiler or something else - see radiator not heating up
One Safety Check Worth Doing
While you're at the boiler, glance at the flame through the viewing window if it has one - it should burn crisp blue. A lazy yellow or orange flame, or sooty marks around the casing, can point to incomplete combustion. Stop using the appliance if safe, go outside and call the gas emergency service: 0800 111 999 in Great Britain or 0800 002 001 in Northern Ireland. For LPG, contact your supplier. Seek medical help if you feel unwell.
If it's hot water specifically that's gone, our no hot water checklist is the place to start, and the boiler repair cost guide shows what each fix runs to. No heat on a cold night? Get an emergency heating engineer on the way.