The short version
- Short cycling on and off in minutes usually means poor circulation or an oversized boiler
- Lockout after a few seconds of firing usually means ignition or flame sensing
- Cutting out only on very cold mornings often means a frozen condensate pipe
- Repeated resets on the same code hide the fault and solve nothing
Which pattern do you have
Time it and note what the display shows. The pattern narrows the cause more than any single symptom.
- Fires and cuts out within seconds, with a lockout code, points at ignition, electrodes or flame sensing
- Runs a few minutes, gets very hot then stops, points at circulation, a blocked filter, a failing pump or a stuck valve
- Cycles on and off constantly at low demand, points at boiler sizing or control setup
- Only fails in freezing weather, points at the condensate pipe outside
- Cuts out and pressure has dropped, points at the sealed system rather than the burner
What you can safely check
Check the pressure gauge, feel whether the radiators are heating evenly or only near the boiler, check the room thermostat is not sited above a radiator or in direct sun, and in cold weather check the outside condensate pipe. All of that is outside the appliance and safe.
Short cycling and why it costs you money
A boiler that fires for two minutes and stops, over and over, burns more gas and wears the ignition components far faster than one long steady run. It is often a control or sizing issue rather than a broken part, and setting the boiler up properly with modulating controls and correct flow temperatures usually settles it.
Where it needs a Gas Safe engineer
Ignition electrodes, gas valves, fans, air pressure switches, flame sensing, pumps and printed circuit boards are all behind the casing and are Gas Safe work. Do not remove the case, do not attempt to clean electrodes, and never bypass a safety device. If the boiler locks out repeatedly, leave it off and book it in.
Common questions
Why does my boiler lock out then work fine after a reset?+
That is typical of an intermittent ignition or flame sensing fault. It will get worse, so it is better diagnosed while the pattern is still readable.
Is a boiler that keeps cutting out dangerous?+
The lockout itself is a safety feature working correctly. The underlying fault still needs a registered engineer, and any smell of gas or fumes should be treated as an emergency.
Could a dirty magnetic filter cause this?+
Yes. Restricted circulation makes the boiler overheat and cut out, and a clogged filter or sludged radiators are a common cause.
Is it worth repairing an older boiler that keeps failing?+
Sometimes. We will tell you which parts have failed and what is likely next, so you can weigh a repair against a new installation honestly.
Boiler cutting out again?
Give us the fault code and the pattern and we will diagnose it properly rather than just resetting it.