Heating Won't Turn Off? Causes and How to Stop It

If your heating won't turn off, either something is still asking for heat or a valve is letting heat through when it shouldn't. The first is usually the controls: a programmer clock that's wrong, a setting left on constant or boost, or a room thermostat that's set high or has lost its signal. The second is a fault: a motorised zone valve stuck open on a system with a hot water cylinder, or a sticking diverter valve on a combi. Some things that look like a fault are normal, such as the pump running on for a few minutes after the burner stops. Work through the controls first. If everything is off and the radiators still heat up, it's time to call a heating engineer.

Start with the controls

Worcester's fault-finding table for its Greenstar CDi Compact boiler gives a one-line answer for "heating stays on for too long": the clock is set wrong. That's the most common cause, and the easiest to fix.

• Clock time. After a power cut or when the clocks change, some programmers lose the time or stay on the old one, so the heating comes on and goes off at the wrong times. Check the time on the display matches the real time.
• Mode. Programmers usually have Auto, On (sometimes "constant" or "24 hours") and Off. If heating is set to On, it runs whenever the thermostat wants heat, whatever the timer says.
• Boost or advance. A boost adds an extra hour or more. An advance jumps to the next on period. Both are easy to press by accident.
• Smart controls. Check the app for a schedule, a holiday mode or another person's override. Some systems also switch to a default schedule if they lose the internet.
• The boiler itself. Some boilers have their own heating on/off setting and a built-in timer as well as the wall controls. Both have to agree.

Room thermostat problems

The room thermostat switches the heating on when the room is below its setting. If the heating keeps running, check:

• The setting. Is it higher than the room will ever reach? Somewhere between 18°C and 21°C is typical.
• Where it is. A thermostat in a cold hallway by the front door, or in a room where every radiator is turned down, will keep calling for heat because that spot never warms up. A thermostat near a radiator or in sunlight does the opposite.
• Batteries and signal. Wireless thermostats talk to a receiver near the boiler. Flat batteries or a lost link can leave the receiver calling for heat. Change the batteries and check the receiver's lights against its manual. Our guide to how room thermostats work explains the different types.
• A failed thermostat. Turn it right down. If you don't hear a click, or the heating doesn't stop within a few minutes, the thermostat or its wiring may be at fault.

Radiator valves matter too. If a TRV in the thermostat's room is turned down, that room stays cold and the heating keeps running to warm it. Our guide to TRV settings explains how to set them. Our boiler thermostat and heating controls pages cover replacing or upgrading them.

Stuck motorised or diverter valves

If the controls say off and the radiators still get warm, the likely cause is a valve that isn't closing. Which one depends on your system. Our guide to types of central heating systems helps if you're not sure what you have.

Systems with a hot water cylinder

System and regular boilers heat the radiators and the cylinder through motorised valves. An S-plan has a separate valve for heating and for hot water. A Y-plan uses one three-port mid-position valve. When the hot water is on and the heating is off, the heating side should stay shut.

If the radiators warm up whenever the hot water runs, the heating valve is probably stuck open or not closing fully. Motorised valves have a head that drives a spindle, and either part can stick. Some have a manual lever that can be left in the open position after draining or maintenance. If yours has one, check it isn't latched open. A valve that's stuck is a repair for an engineer: it may need a new head or a full valve, and that can mean draining down.

The problem can also be the other way round: a relay in the programmer or wiring centre that doesn't switch off, which keeps the heating valve powered. An engineer can test which it is.

Combi boilers

A combi uses a diverter valve inside the boiler to send heat either to the radiators or to your hot taps. If it sticks partly open, the radiators get warm every time you run a hot tap, and the hot water may be lukewarm. It's a common combi repair and has to be done by a Gas Safe engineer. If your problem is the reverse, with hot water but no heating, see our guide to no hot water but heating works and our no heating page.

Things that look like a fault but aren't

• Pump overrun. Many boilers keep the pump running for a few minutes after the burner stops to clear heat out of the boiler. The radiators may stay warm for a short time. That's normal.
• Frost protection. Many boilers and some controls fire the heating in very cold weather to protect the pipes, and some systems have a separate frost or pipe thermostat. If the heating comes on only on freezing nights, that's probably why.
• Gravity circulation. On older open vented systems, hot water from the boiler or cylinder can rise into upstairs pipes and radiators on its own, even with the pump off. Upstairs radiators or towel rails get warm while hot water is heating. It isn't dangerous, but an engineer can fit a valve to stop it if it bothers you.
• Heated towel rails. In some homes the towel rail is plumbed onto the hot water circuit on purpose, so it's warm whenever the hot water is on.

How to stop it for now

1. Set the heating channel to Off on the programmer and turn the room thermostat right down.
2. If there's a heating on/off setting on the boiler itself, turn that off as well.
3. If the radiators still heat up, turn the TRVs down to their frost setting in rooms you don't need warm.
4. As a last resort, switch the boiler off at its fused spur. You'll lose hot water too, and the pump can't run on to cool the boiler, so only do this when the other steps haven't worked. Switch it back on once an engineer is booked or you need hot water.

Don't try to take a motorised valve apart or open the boiler. Anything inside the boiler needs a Gas Safe registered engineer.

When to call an engineer

Book a heating engineer when the controls are all off and the radiators still get warm, when the radiators heat up every time you use hot water, or when the thermostat clicks off and nothing happens. It's worth doing sooner rather than later: heating that never switches off wastes gas, and a valve that's stuck part open usually gets worse.

When you call, tell us whether you have a combi or a hot water cylinder, when the radiators get warm (all the time, with hot water, or only at night), and what controls you have. That's usually enough to know whether it's the controls, a zone valve or the boiler. Our central heating repair service covers valves, controls and wiring across London.

We charge £95 an hour for labour, plus a £60 call-out that's waived when the job runs over 2 hours. Parts are extra and we confirm the price before any work starts. See our pricing page for how jobs are charged.

If the heating only comes on by itself on cold nights, see our guide to frost stats and boiler frost protection for how to check the setting.

Frequently Asked Questions