SDP journal
Why Does My Boiler Keep Turning Off?
You’ve just got the house warm and the boiler cuts out again, or it fires up, runs for a minute and stops. A boiler that keeps turning off is usually protecting itself. The most common causes are low pressure, a frozen or blocked condensate pipe, poor circulation from sludge or a pump fault, and thermostat or control problems. A few checks are safe to do yourself. If it keeps happening, ring us on 01227 200 596 and we’ll arrange a boiler repair in Canterbury or East Kent.
Lockout or short cycling?
It helps to know which you’re dealing with.
- Lockout: the boiler stops and shows a fault code or warning light, and won’t restart until it’s reset.
- Short cycling: the boiler turns on and off repeatedly without a fault showing, often every few minutes.
Lockouts usually point to a specific fault. Short cycling is more often a sign the boiler is oversized, the controls are set up poorly or water isn’t circulating properly.
Checks you can safely make
- Look at the pressure gauge. Most sealed systems should read around 1 to 1.5 bar when cold. If it’s low, top up using the filling loop as your manual shows.
- Check the condensate pipe in freezing weather. If it’s frozen, thaw it gently with warm water.
- Check the thermostat. Make sure it isn’t set just above room temperature, sitting in a draught or next to a heat source, and that the batteries aren’t flat.
- Check radiator valves are open, especially after decorating.
- Note the fault code and look it up in your manual.
- Reset once. If it locks out again, stop and call an engineer.
Never remove the boiler casing. If you smell gas, turn off the supply at the meter if it’s safe, open windows and call the National Gas Emergency Service on 0800 111 999.
The most common causes
Low pressure
When the pressure drops too low, the boiler locks out to protect itself. If you have to top up regularly, there’s a leak or a faulty pressure relief valve or expansion vessel.
A blocked or frozen condensate pipe
Condensing boilers shut down when condensate can’t drain. In winter, freezing is the usual cause. At other times, debris can block the trap or pipe.
Overheating from poor circulation
If water isn’t flowing properly, the heat exchanger gets too hot and the boiler cuts out. Sludge, a failing pump, closed valves or air in the system can all cause it. You may also hear kettling.
Thermostat and control faults
A faulty or badly placed thermostat can switch the boiler on and off far more than it should. Wiring faults and failing programmers can do the same.
Ignition and flame detection problems
If the boiler can’t light or doesn’t detect the flame, it locks out. Causes include a faulty ignition electrode, flame sensor or gas valve, or a problem with the gas supply. These need a Gas Safe engineer.
An oversized boiler
A boiler much bigger than the home needs reaches temperature quickly, switches off, then fires again. It works, but less efficiently and with more wear.
Boilers cutting out in Canterbury and East Kent
East Kent is a hard water area, and limescale on the heat exchanger can lead to overheating and cut-outs. Homes around Canterbury, Whitstable and Herne Bay with older systems may also have sludge restricting flow. If that’s the cause, a powerflush may be part of the fix.
Frequently asked questions
Is it safe to keep resetting my boiler?
One reset is fine. If it locks out again, stop. Repeated resets won’t fix the underlying fault and can make some problems worse. Note the fault code and call a Gas Safe engineer, who can diagnose what’s causing the lockout.
Why does my boiler turn off when the hot water is on?
On a combi, the boiler switches between heating and hot water. If it cuts out when you run a tap, causes include low pressure, a diverter valve fault, poor flow or a scaled heat exchanger. If it happens often, get it checked.
Can a service stop my boiler cutting out?
A service often finds the cause, such as a blocked condensate trap, worn components or poor combustion. It’s also the right time to check the expansion vessel and pressure. Regular servicing reduces the chance of lockouts, and any worn parts can be replaced before the coldest weather.
Boiler still cutting out?
If your boiler keeps turning off and the simple checks haven’t helped, give us a call on 01227 200 596 or drop us a message and we’ll find out what’s causing it.