Boiler Won’t Turn Off: Find and Fix These Causes

Heating not coming on is usually a more common problem in climates like the UK where the average temperatures are not very high.  But a boiler and heating system that isn’t turning off and you sweating in the summer heat can be an issue too, not only affecting comfort but wasted energy and increased fuel bills.

Why won’t my boiler turn off?

The main cause of a boiler not turning off is a thermostat fault where the sensor isn’t working or the message isn’t getting to the boiler. This could be because of weak batteries. Other causes are boiler programmer issues, or internal wiring faults. Occasionally, faults can happen when repairs have not been done properly.

1. Faulty thermostat

Heating on when the thermostat is off.

First, replace the batteries on the room thermostat because if they are weak, the message may not be sent to the boiler to switch off. 

Check the thermostat to see if it has a frost setting where if the temperature drops below the setting, the boiler will fire up.  Make sure the thermostat isn’t in a cold place and sending a message to keep the boiler on.

Fix. If the system won’t turn off and heat keeps being delivered, set the thermostat to its lowest temperature setting and wait a few minutes. Try changing the batteries on the room thermostat.

2. Boiler Programmer issue

A programmer allows you to set your heating times on and off during the day and week.  You can pre set the times and the boiler will fire up and shut off at these times. 

Once a thermostat fault has been discounted, this will probably be the next stage of investigation by the gas engineer who would also check the wiring and connections with the other components.

Fix. You can get heating cover with Hometree at an affordable price. For more information click here.

 3. Issue with Thermostatic Radiator Valves (TRV)

photo of trv closeup

 In the summer when you don’t need the heating on but still require the hot water, many people turn the TRV to the zero or off setting and this should shut the valve completely.  But sometimes these valves don’t close properly and some heat can get into the radiator. 

Fix. To fix this, you can turn off the lockshield valve at the other end of the radiator and this should stop residual heat seeping through. 

Remember to count how many turns you made to turn off the lockshield because when you want the heating back on in winter, the radiators will need to be balanced and each of these valves turned on as they were before.

4. Boiler wiring or printed circuit board  

A wiring issue could be the cause where even when the programmer is off, power is going to the boiler through the microswitch instructing it to continue heating. 

Fix. This is an internal boiler issue. A gas engineer will be able to check this once other causes have been discounted. If you don’t already have boiler cover, we recommend Hometree for all your boiler requirements.

boiler pcb repair image

5. Problem with motorised valve (3 port valve)

Heating comes on with hot water

A motorised valve is usually found near the hot water cylinder and controls what type of hot water is sent – either from the boiler to heat the radiators or from the cylinder to the hot taps.

If this valve is stuck and there is a demand for heating at the same time as the valve is in the hot water position, the valve won’t close completely and will allow some hot water to still pass through to the radiators and warm them up.

Fix. Usually the fix for this is to drain the heating system down, remove the 3 port valve and replace it with a brand new one and refill the system with water. You can call a plumber if you don’t want to do this yourself.

6. Issue following a repair

If any changes have been made to the heating system an issue can arise, especially with system boilers that have a cylinder. After a repair, a plumber or even someone working on it themselves puts a pipe fitting on the incorrect part of the flow and return pipework coming from the cylinder.

So instead of the water going back to the return pipe of the boiler, it can sometimes circulate in the opposite direction to head towards the radiators.  In this case, you will need to get a plumber to investigate and fix it.

The above issues are the most likely causes of heating not turning off and with most of them, you will need a qualified gas engineer to find and fix the fault.  If your boiler isn’t in warranty, why not get home heating cover with Hometree

Hometree offers customers peace of mind with home care packages for your boiler, central heating, plumbing, drains and home electrics all at an affordable monthly or annual cost.

Hometree’s aim is to take the stress out of boiler servicing and home maintenance with unlimited call-outs and a 24/7 helpline, as well as a no price-hike promise. 

Is it safe to turn the boiler off at the mains?

It is safe to turn your boiler off at the mains as long as there are no other issues with it. A combi boiler turns itself off anyway for various reasons like when there is no flame present or low water pressure.


These are potential causes of heating not turning off:

  1. Thermostat faults.
  2. Boiler Programmer issues.
  3. TRV (Thermostatic Radiator Valve) problems.
  4. Boiler wiring faults.
  5. Motorised Valve is stuck
  6. Repair not done properly.

*The information in this article should be used for general guidance only.  Full details are on the link in the footer to our disclaimer page.  Always discuss your requirements with a competent and suitably qualified professional before undertaking any work.