Advice from Paul · Gas Safe #221708
In short: A boiler usually stops working because of low pressure, a tripped or locked-out fault, no power or gas, a thermostat problem, or a failed part like the pump or diverter valve, and many of these show a fault code on the display.
A boiler that suddenly stops is one of the most stressful things to go wrong in a home, especially in winter. The good news is that the causes usually fall into a handful of common categories, and some are things you can safely check yourself before calling anyone out.
Here is the honest run-through from a Gas Safe engineer with 40 years on the tools. A couple of these you can look at yourself; anything involving gas or opening the boiler up is a job for a registered engineer, not a YouTube video.
Before ringing anyone, it is worth a two-minute look at the simple stuff, because sometimes that is all it is.
01
Check the pressure gauge
If the needle is below about 1 bar (usually in the red or near the bottom), low pressure may be stopping the boiler firing. Many boilers can be topped up via the filling loop, if you know how, but if it keeps dropping you have a leak somewhere and need it looked at.
02
Check the power and thermostat
Make sure the boiler has power, the fuse or switch has not tripped, and the thermostat is calling for heat and has working batteries. It sounds obvious, but a flat thermostat battery stops many boilers.
03
Check other gas appliances
If your gas hob will not light either, the issue may be your gas supply or a prepayment meter that has run out, not the boiler itself.
04
Note any fault code
If the display shows a code like F22, F28, L2 or EA, write it down. It tells the engineer a lot before he even sets off.
If the simple checks do not sort it, the cause is usually one of a handful of faults: a boiler locked out on a safety fault, a failed pump, a stuck diverter valve, a faulty sensor or PCB, or an ignition problem. These need a Gas Safe registered engineer to diagnose and fix safely.
Resetting a boiler once or twice is fine, but if it keeps locking out, stop. Repeated lockouts mean a real fault the boiler is protecting you from, and hitting reset over and over will not fix it.
Rather just get it sorted?
You get Paul on the phone, a Gas Safe engineer with 40 years behind him, not a call centre. He will give you a straight answer and a fair fixed price. See boiler repair for how he can help.
Straight answers
Once or twice is fine, but if it keeps locking out, stop and call an engineer. Repeated lockouts point to a genuine fault the boiler is protecting you from, and resetting will not fix it.
Low pressure itself is not dangerous, it just stops the boiler working. But if the pressure keeps dropping after you top it up, there is a leak in the system that needs finding and fixing.
Each make has its own codes. Note down the code and give it to Paul when you ring, after 40 years he can usually tell you roughly what it points to before he even sets off.
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Honest advice, then a proper fix
Forty years on the tools, Gas Safe registered, and the fella who quotes it is the fella who does it. No call centre, no pushy sales.