No heating but hot water works: what to check
Quick summary
If hot water works but radiators don’t, start with thermostat/programmer settings, then confirm whether the boiler receives a heating demand.
Safety first
- Smell gas or suspect a leak: leave the area and call 0800 111 999.
- Do not remove boiler covers or interfere with gas components.
- If water is leaking near electrics, isolate power only if safe.
Full checklist: Safety guidance
What to check (in order)
- Set the thermostat higher than room temp and ensure heating is ‘on’ at the programmer.
- Open TRVs on at least a couple of radiators.
- Does the boiler fire on heating demand? Any fault code?
- Check boiler/system pressure (sealed systems).
- If you have a two-channel timer, ensure CH channel is enabled.
What the result means
- Boiler fires for HW but not CH: likely controls/demand chain.
- Some radiators warm: air, TRVs, balancing, or restrictions.
- Fault on CH demand: record code; often points to pump/overheat/flow.
What you can safely do
- Turn the thermostat above room temperature and make sure heating is on at the programmer.
- Open a couple of radiator TRVs fully.
- Check system pressure if you have a sealed system.
- Reset once only if your boiler manual allows it and there are no danger signs.
When to call a professional
- Controls calling for heat but boiler won’t fire.
- Repeated lockouts/overheat symptoms.
- Leaks near electrics.
Engineer notes
Trace demand path: stat/programmer → zone valve end-switch → boiler call. Differentiate ‘no demand’ vs ‘demand present’. Document flow temp response and any overheat behaviour.
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