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Quick answer
If your central heating keeps running when you have switched it off, something is still telling the boiler to fire or letting heat reach the radiators. Check the programmer and room thermostat settings first, including any override or boost. Then consider frost protection, a faulty thermostat or wireless receiver, a zone valve stuck open, a diverter valve fault on a combi, or a wiring problem after new controls were fitted. Heat reaching radiators while the boiler is only heating water is a separate valve issue.
Key takeaways
- Check programmer mode, boost and holiday settings before anything else.
- Frost protection legitimately fires the boiler in very cold weather.
- A failed wireless thermostat or receiver can keep calling for heat.
- A zone valve stuck open keeps radiators hot whenever the boiler runs.
- On combis, radiators warming with hot water use points to the diverter valve.
Step 1: controls
- Is the programmer set to “off”, or is it on “constant” or “always”?
- Is there a boost or advance function active?
- Is the room thermostat set above room temperature?
- Is a smart thermostat app or schedule overriding your settings?
Resetting the programmer to a simple schedule often solves it.
Step 2: frost protection
Many boilers and some thermostats have frost protection that fires the boiler when temperatures drop very low. That is normal and protects your system. See boiler frost protection setting explained.
Step 3: thermostat or receiver faults
Wireless thermostats have a receiver near the boiler. If the thermostat’s batteries are low, or the receiver has failed in the “on” position, the boiler may keep firing. Change the batteries and check the receiver lights. A failed wired thermostat can also keep the circuit closed.
Step 4: zone valves
On system and regular boilers, the heating zone valve opens when there is demand and closes when there is not. If it sticks open, radiators heat whenever the boiler fires for hot water. If its microswitch sticks, it can keep the boiler firing. See what a zone valve is.
Step 5: combi diverter valve
On a combi, if radiators get warm when you run a hot tap, the diverter valve is likely at fault. See radiators hot when the heating is off.
Step 6: wiring
If the problem started after a new programmer or smart thermostat was fitted, the wiring may be incorrect. An engineer can check the wiring against the system plan.
What to do in the meantime
If the heating will not turn off and you need to stop it, turn the boiler off at its fused spur, but remember you will lose hot water too. Do not leave it off in freezing weather without protecting pipes.
Book with Gasmaster
Heating stuck on? Gasmaster Plumbing & Heating, Gas Safe registered (220932), fixes controls, valves and central heating faults across Stoke-on-Trent, Newcastle-under-Lyme and Biddulph.
Frequently asked questions
Why does my boiler keep firing when the heating is off?
It may be frost protection, a hot water demand, or a controls or valve fault.
Can a faulty thermostat keep the heating on?
Yes. A thermostat or wireless receiver stuck in the “call for heat” state is a common cause.
Is it dangerous if the heating won’t turn off?
Not usually dangerous, but it wastes gas and can overheat rooms.
Sources
- Energy Saving Trust, heating controls guidance (energysavingtrust.org.uk)
- Manufacturer wiring guides for S-plan and Y-plan systems
- Gas Safe Register (gassaferegister.co.uk)
Related services
Abdul runs Gasmaster Plumbing & Heating and has worked on boilers, heating and gas appliances across Stoke-on-Trent since 2005. He is Gas Safe registered (reg. 220932), and these articles come from his day to day work in homes and businesses across Staffordshire, Cheshire and Derbyshire.
