The short version
- Flat thermostat batteries are the single most common cause
- Wireless thermostats can lose pairing after a power cut
- A seized motorised valve stops the heating circuit silently
- Check the programmer's schedule and any holiday mode first
Work through the chain
The heat demand travels from the thermostat, through the programmer, to the valve, then to the boiler. Test in that order.
- Replace the room thermostat batteries and turn the set point well above room temperature
- Check the programmer is in a heating period, not off or in holiday mode
- Re-pair a wireless thermostat with its receiver if it's lost the link
- Listen for the motorised valve moving when you call for heat
- Check the TRVs aren't all closed and the pins aren't seized
Motorised valves
On systems with a cylinder, a two-port or three-port valve directs flow. A failed motor or a seized spindle means the boiler never gets the end-switch signal, so nothing fires even though everything else is fine. Replacing a valve head is a routine job.
Upgrading while you're at it
If the controls are ancient, replacing them with a modern programmable or smart thermostat gives you better comfort and usually better efficiency than nursing a thirty-year-old timer.
Common questions
Why does hot water work but not heating?+
Because they're separate demands. A heating-only failure points at the heating control chain.
Can you fit a smart thermostat?+
Yes, we install and commission modern controls with the boiler set up correctly for them.
Is a seized valve expensive?+
Usually the head is replaceable without cutting into pipework, which keeps it affordable.
Could it be the boiler after all?+
It can be. We test the demand signal at the boiler to prove which side the fault is on.
Heating not firing up?
We'll test the control chain and prove where the fault sits.