Boiler Not Working? The Six Most Common Faults
What the fault code is really telling you, what's safe to try, and when to stop.
Low pressure
The gauge below 1 bar is the most common no-heat cause. Repressurise via the filling loop to 1.2–1.5 bar. Needing to do it more than every few months means water is going somewhere, that's a leak, not a habit.
Frozen condensate pipe
The white overflow pipe outside freezes in a cold snap and locks the boiler out. Pour warm (not boiling) water along it, reset, and it usually comes straight back. Lag it so it doesn't recur.
Everything else
Failed diverter valves, seized pumps, faulty ignition and scaled heat exchangers all present as codes on the display. The code plus the make is genuinely useful information, have it ready when you call. Anything behind the case is Gas Safe territory: not a DIY frontier.
When to stop trying
Smell gas, see soot marks, or hear the CO alarm, stop, open windows, call 0800 111 999 before anyone else. Nothing on a screen is worth testing past that point.
Reading the fault code properly
The code plus the make and model is genuinely useful diagnostic information, and having it ready when you call often means the engineer arrives with the right part on the van. Photograph the display rather than transcribing it, codes like F.28 and E128 are easy to mis-hear and lead to the wrong part being carried.
Faults that are not the boiler
A tripped RCD, a prepay meter out of credit, a timer wrong after a power cut, a room thermostat with flat batteries, or a frozen condensate pipe. Between them these account for a substantial share of "boiler broken" callouts, and every one is free to check before you spend money on anybody attending.
How long a boiler should last
Twelve to fifteen years for a well-serviced condensing boiler, less in hard water without scale protection. Once repairs exceed half the cost of replacement on a unit past ten, replacement usually wins on cost alone. Below that, repair, and be wary of any firm whose first answer to a fault code is a new boiler.
Five checks that fix a surprising share of no-hot-water mornings for free.
Valve, spindle, tail or the panel itself, each one leaks differently, and only one of them means a new radiator.
A sealed system does not consume water. If you are topping up, it is going somewhere, and where matters.
Immersions, multipoints and wall heaters fail in predictable ways. What to check before replacing anything.
Sediment makes cylinders rumble, slows heating and kills elements. Flushing it is routine maintenance.