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Why are my radiators getting hot when the heating is off?

With the cost of living continuing to rise, it is more important than ever to conserve as much energy as possible and heat our homes efficiently. That’s why when radiators are getting hot when the heating is off, you could be wasting energy and cost by heating rooms you are not using. 

Or, in the summer your home could be uncomfortably warm if the radiators are getting hot when you don’t want them to. In this guide, we will cover why radiators get hot when the heating is off and what to do to fix the issue. It’s more common than you might think!

Why are my radiators hot when the heating is off?

There are a couple of system faults that could be causing your radiators to heat up when the heating is turned off. For example:

1. Diverter valve problem

If the diverter valve is broken or stuck in a combi boiler, it can cause your radiators to get hot when the heating is off. But how does it work? 

When the boiler is turned on, the diverter valves control the direction of the hot water through the heating system. You can adjust the settings on the dial on the front of your boiler. The water can be directed to the radiators, hot water tap, or both.

The diverter valves open and close depending on the direction. So when you want to heat up your radiators, the tap diverter valve will close to allow hot water to head to the radiators instead of the taps. 

To put it simply, the system works in the same way as a bath with a pair of taps and a showerhead attached where you can choose where the water comes from.

plumber fixing a boiler

Why do the diverter valves get stuck?

Since the diverters are constantly opening and closing each day and night, they can get worn out, damaged, or blocked with sludge. This can cause them to get stuck in the same on, off, or mid position. This means that hot water from the boiler might keep running through your radiators and heating them up even though the heating is turned off. 

If you have noticed that the radiators are getting hot when the hot water is on, this probably means that the diverter valve is stuck in the mid position. This will continue to happen even if your central heating thermostat tells you the heating is turned off. This can also mean that your hot water tap isn’t getting as hot as it should do. It can also cause your hot water taps to only work when the heating is on.

How to fix a stuck diverter valve

If you think you might have a problem with a broken or stuck diverter valve, we would always advise that you get in touch with a Gas Safe Registered engineer. The engineer will have the equipment to test your boiler and work out whether the diverter valve is the issue. 

If it turns out that the diverter valves are to blame, they can sometimes be fixed by cleaning. Otherwise, they will need to be replaced. The diverter valve is usually on the outside of the boiler and can be cleaned or replaced pretty quickly. 

You should be able to get a new diverter valve for free if your boiler is still under warranty. You will only be charged for the labour cost unless you call out a manufacturer-approved engineer.

2. Check valve problem

If your radiators are getting hot when the heating is off and the diverter valve is working, there might be an issue with the check valve. The check valve is a device used inside older boilers that stops the central heating system from staying hot by stopping the natural convection. 

In more modern systems an electrically controlled solenoid valve is used to control the flow of heated water instead. When the check valve fails or solenoid valve becomes blocked or breaks, the heat from the boiler rises and travels to your radiators so they will get hot even when the thermostat is off. 

Whether you think there is an issue with the check valve or motorised valve, you will need to contact a Gas Safe Registered engineer to test the system safely and replace parts if necessary.

Why does my boiler keep firing up when the heating is off?

If you hear your combi boiler firing up every so often when the heating is off, it is totally normal. The boiler does this even if you are not calling for heat or hot water. This preheating helps the boiler ensure you have hot water when you turn it back on. If not, you might have to run your tap for a while until you get hot water which could increase your energy usage and cost. 

Why is my bathroom radiator on when the heating is off?

In some hot water systems, the bathroom radiator or heated towel rail is connected to the hot water circuit. This means that the bathroom radiator comes on with the hot water even if the heating is switched off. 

This is generally considered an inefficient way to heat your bathroom. Instead, you might want to consider a dual fuel radiator or towel rail that can be both used with the central heating and independently as an electric heater.


dual fuel towel rail in a bathroom

Why are my radiators not turning off?

To conclude, if your radiators are not turning off when the heating is off there is likely a problem with the diverter, check, or solenoid valve. If these valves get stuck they will keep sending hot water to the radiators even when the heating thermostat is off. You might also notice that your hot water taps are lukewarm.

What to do when the heating is off and the radiators are on

As we mentioned earlier, it is always best to contact a Gas Safe Registered engineer when your heating is off but your radiators are on. It is not a job that we would advise looking at yourself unless you are a qualified heating engineer. It is a good idea to seek professional advice as soon as you notice the problem to help minimise your energy usage and cost. 

Frequently Asked Questions

If your home radiators will not switch off even when the central heating isn’t on, the most likely cause of the issue is troubles with a diverter or check valve.

Should the valves become damaged or blocked, they can continue to transport hot water to your radiators even when the thermostat is switched off. Lukewarm water taps are another sign that your radiators might be working overtime.

For a more detailed insight and tips on how to rectify the problem, explore our dedicated blog, Why are my radiators getting hot when the heating is off?

It is commonplace for a combi boiler to fire up now and again even when the central heating is switched off. The boiler can tend to do this even when heat or hot water is not being demanded by or distributed to your home radiators or alternate heating devices.

This method of pre-heating enables your boiler to guarantee hot water is available as soon as it is turned back on. Otherwise, you might need to run your taps for a while until the hot water supply returns, which could cause your energy use and bills to spiral in turn.

To find out more, visit our related blog, Why are my radiators getting hot when the heating is off?

Most commonly, issues with valves lead to radiators working as usual despite the heating being switched off. Especially in warm summer climes and with a massive emphasis placed on keeping energy bills as low as possible, the prospect of home radiators turning on whilst the central heating is switched off is unappealing.

The problem will typically stem from troubles with diverter valves or check valves, with the latter often associated with older boiler or central heating system models. For a more detailed insight on why radiators seem to switch on by themselves, and how to combat the problem, take a look at our dedicated blog; Why are my radiators getting hot when the heating is off?

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