Boiler not working in Surrey

A boiler that's stopped working usually comes down to one of a handful of causes: low pressure, a tripped electrical supply, a faulty thermostat, a stuck diverter valve, or a fault the boiler itself is flagging with an error code or a locked-out light. Which one it is often depends on whether you've lost heating, hot water, or both, so that's the first thing worth working out before you call anyone.

This page covers the common patterns, what to check yourself, and when it's a job for a Gas Safe registered engineer.

What would cause a boiler to keep shutting off?

A boiler that keeps shutting off and restarting is usually protecting itself from a fault: low water pressure, a blocked condensate pipe, air in the system, or a sensor reading something's wrong. Most modern boilers show an error code or a flashing light when this happens, which is the fastest way to narrow down the cause.

If restarting the boiler brings the heating back briefly before it cuts out again, that pattern points to pressure or a sensor fault rather than something electrical. Check the pressure gauge first: see our low pressure boiler guide for what the reading should be and what to do if it's off.

My radiators are working, but I have no hot water. What could be the problem?

Heating that works but no hot water usually points to a faulty diverter valve, the part that switches the boiler between heating radiators and heating your hot water taps. On a combi boiler, this is a common and fairly affordable fix. It can also be a failed thermostat or a problem with the hot water sensor.

A less common cause is a broken plate heat exchanger on a combi boiler, which handles the hot water side specifically. An engineer can tell the difference quickly once they've had a look at the boiler's fault history and run a few checks.

What is the first thing to check when there is no hot water?

Check the boiler's display for an error code or a locked-out light first, then check the pressure gauge: most combi boilers need 1 to 1.5 bar when the system is cold. If the pressure's fine and there's no error showing, check the room thermostat and hot water programmer are set correctly and haven't been knocked.

If none of that explains it, the fault is likely inside the boiler, a stuck diverter valve or a failed part, and it's time to book an engineer rather than keep troubleshooting.

Why is one of my radiators not heating up even though the heating is on?

One cold radiator while the rest of the system works is almost always trapped air or a build-up of sludge in that radiator, not a boiler fault. Bleeding the radiator usually clears trapped air. If it's cold at the bottom rather than the top, that's more often sludge, which bleeding won't fix.

If several radiators are affected, or bleeding doesn't help, the system may need a power flush, a deeper clean that clears sludge throughout the whole system rather than one radiator.

Questions people ask

Why would my hot water not work but my cold water does?

This points to the boiler rather than your water supply, since cold water doesn't pass through it. The most likely causes are a faulty diverter valve, a broken hot water sensor, or (on a combi boiler) a failed plate heat exchanger. A Gas Safe registered engineer can diagnose which one from the boiler's fault history.

Why is my heater turned on but no heat is coming out?

If the boiler's running but radiators stay cold, check the system pressure and the room thermostat setting first. If both look right, the cause is usually trapped air, a failed pump, or a stuck valve inside the boiler preventing hot water from circulating to the radiators.

Why am I getting hot water but my radiators aren't heating up?

This is the reverse pattern to a diverter valve stuck on hot water, and it points to the same part: the valve that switches the boiler between heating and hot water. It can also be caused by a failed central heating pump, or the room thermostat being set too low or switched off.

Why would heating not work but hot water does?

Usually a thermostat or programmer issue rather than a boiler fault: check the heating is actually switched on and the room thermostat is set above the current room temperature. If that's not it, a faulty pump or a stuck valve inside the boiler can also cause this pattern.

How do I know if my diverter valve is faulty?

The main sign is heating and hot water interfering with each other: hot water but cold radiators, or radiators that only heat while a tap is running, or the reverse. A faulty diverter valve usually needs replacing rather than repairing, and it's not a DIY job since it involves draining and working inside the boiler. If you suspect yours after a reset, see our boiler reset not working guide.