Central Heating Not Working: A Sensible Checklist Before You Call
When the heating stops, the fault is somewhere in a chain: the controls have to call for heat, the boiler has to fire, the pump has to move water, the valves have to open, and the radiators have to be able to take flow.
When the heating stops, the fault is somewhere in a chain: the controls have to call for heat, the boiler has to fire, the pump has to move water, the valves have to open, and the radiators have to be able to take flow. Working through that chain in order finds the fault far faster than jumping between symptoms, and several of the steps are things you can safely check yourself in a few minutes.
Start with the controls, not the boiler
More heating callouts than you would expect come down to a programmer that has reverted after a power cut, a room thermostat set below room temperature, a thermostat with flat batteries, or a smart control that has lost its pairing. Turn the thermostat well above the current room temperature and listen for the boiler responding. If there is a hot water setting on the programmer, test that too: hot water working while heating does not is a very useful clue and usually means a diverter or zone valve.
Power, pressure and the obvious
Check the boiler has power and its display is lit. Check the fused spur has not been switched off and no fuse has blown. On a sealed system, look at the pressure gauge — below the normal band and the boiler will refuse to fire, and it also means water has been lost somewhere. Check the gas supply is on and other gas appliances work. If you are on a prepayment meter, check the credit before anything else.
Frozen condensate and lockouts
In cold weather, a boiler that fires briefly then locks out with an error is very often a frozen external condensate pipe. Warm water poured over the exposed pipe and a reset usually restores it. A boiler that locks out repeatedly at any time of year is protecting itself from something specific — poor flow, ignition failure, flue issues — and resetting it over and over is not a fix, it is a delay.
Hot water but no heating, or the reverse
This split is genuinely diagnostic. Hot water fine but no heating on a combi points at the diverter valve or the heating side of the controls. On a system with a cylinder, it points at the heating zone valve, its actuator, or the wiring centre. No hot water but working heating on a combi again points at the diverter or the plate heat exchanger. Telling an engineer which way round it is meaningfully shortens the diagnosis.
Pump and circulation
If the boiler fires and gets hot but the radiators stay cold, water is not circulating. Common causes are a seized pump, a pump running but airlocked, a jammed zone valve, or a system so sludged that flow has collapsed. A boiler that heats up quickly and then cuts out on overheat is a classic circulation failure rather than a boiler fault as such.
Some radiators cold, most warm
That is not a heating breakdown, it is a distribution problem: air at the top, sludge at the bottom, a stuck TRV pin, a lockshield closed too far, or a system that has never been balanced. It is worth fixing but it is a different job from a system that is not producing heat at all, and describing it accurately gets you the right appointment.
Heating down and checks not solving it?
Tell us what you have already checked and what the boiler is doing, and we will pick up the diagnosis from there.
Questions we get asked
How many times can I reset a boiler?
Once, to clear a one-off lockout. If it locks out again, something is triggering it and repeated resets only postpone the diagnosis.
Why is the boiler firing but the radiators stay cold?
Water is not circulating. Typical causes are a seized or airlocked pump, a jammed zone valve, or heavy sludging restricting flow.
Hot water works but heating does not — what is that?
On a combi, usually the diverter valve or heating controls. On a cylinder system, usually the heating zone valve, its actuator or the wiring centre.
Should I top the pressure up myself?
A single top-up to the normal band is reasonable. Needing to do it repeatedly means water is escaping and that needs finding, not topping up.
Is no heating an emergency?
In freezing weather with vulnerable occupants in the property, treat it as urgent. Otherwise it is normally something that can be booked in.