Boiler keeps turning itself off? Here's what's happening

A boiler that shuts down on its own is usually protecting itself. Something has gone outside its safe operating range and it has stopped rather than carry on. That is the system working, not failing - but you still need to know why.

Check these first (free)

Pressure. Below about 1 bar, most boilers cut out. Top up with the filling loop to 1.2 bar cold. If it drops again within days, you have a leak somewhere.

The condensate pipe, if it is cold outside. A frozen condensate is the single most common winter cut-out. It is usually a white plastic pipe running out through a wall. Warm water poured along it, or a hot water bottle held against it, often clears it in twenty minutes.

The room thermostat batteries. Genuinely. A thermostat with flat batteries stops calling for heat, and the boiler looks like it has died.

Short-cycling

The boiler fires, runs for a minute, stops, then fires again. This is usually a boiler that is oversized for the house, or a system with poor circulation.

It is not dangerous but it is wasteful and it wears the boiler out. If it started recently on a boiler that used to run normally, suspect sludge restricting flow, or a failing pump.

Lockouts with a fault code

A code on the display is the boiler telling you exactly what is wrong, and every manufacturer publishes what they mean. Look yours up before you ring anyone - it changes the conversation, and it tells you whether you are looking at a £120 job or a £600 one.

Repeated lockouts on the same code, on a boiler over ten, is a pattern rather than an incident.