Why Are My Radiators Hot When the Heating Is Off?

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Written By: JustBoilers.com Experts | Last Updated: January 2024

At one time or another everyone has had the misfortune of having to temporarily cope without heating due to a malfunctioning boiler. There is also the flipside whereby you cannot turn down the heat, which is just as uncomfortable, especially during the warmer months of the year.

The problem of radiators on when heating off occurs more commonly than you might imagine. But what causes this to happen? We can provide some reasons for this phenomenon in the following article.

Why is Heating Off But Radiators On?

There are many reasons your heating is turned off but radiators are hot.

Problems With Your Diverter Valve 

Diverter valves open and close to allow or cut off hot water that flows through your heating system and radiators. When hot water needs to be sent from the boiler to radiators instead of the taps, for instance, the tap diverter valve will close.

Why is my heating coming on when the thermostat is off?

Similar to bathtubs that have a showerhead in addition to the normal taps could be the culprit. A diverter valve will direct the flow of water to either the showerhead or the tap, depending on your selection. On the other hand, diverters will go to a ‘mid’ position if water flow is needed for both your hot water system and radiators at the same time.

Because these valves keep opening and closing as required throughout the day, they can get stuck or become damaged. When this happens, hot water may continue to flow through to your radiators – even when your heating is switched off.

If this is the case, get in touch with a qualified engineer to come and take a look at the problem. The Gas Safe Register is a great place to find a local tradesman in your area. They will carry out some tests to check if the diverter valve is the issue or whether there’s another underlying problem.

If the valve were at fault, it would either need to be cleaned or replaced. In circumstances where it needs to be replaced you’re advised to check whether your boiler is still under warranty.

If so, you will likely be able to get a new one at no extra cost (excluding the labour cost, unless a manufacturer-approved specialist is used).

A Broken Check Valve 

Older boilers keep water hot at all times. The hot water then travels through your radiators by natural convection. When you need to heat up your home, the water is pumped from the boiler through to your radiators. Once your home reaches the desired temperature, the heat turns off which causes the pump to stop running.

A check valve is used to stop the natural convection from warming up your home when your heating is switched off. If the check valve is broken or blocked, heat will rise through your system causing your radiators to stay hot.

Once again, contact a qualified professional to come and check what the problem is. After running some diagnostics they’ll be able to fix the issue safely and correctly.

If your boiler is no longer under warranty or is older than 10 years old, however, it may be worth considering the replacement of the entire boiler, instead of the check valve alone.

Different types of radiator valves give far greater control over the individual heat of each room. If you’re unsure how radiators work, we’re here to help.

How to Fix a Broken Valve

Fixing a broken valve typically involves diagnosing the issue, such as leaks, blockages, or wear and tear, and then taking appropriate measures to repair or replace the faulty parts. 


This could involve disassembling the valve, cleaning or replacing components like seals or springs, and reassembling everything securely.


It’s important to ensure that the valve is compatible with the system it’s part of, and that all repairs are done in compliance with safety standards and regulations.


For non-engineers, attempting valve repair on complex systems can lead to further damage or safety hazards. With this in mind, always consult a professional engineer for the repair work.


Why Are My Radiators Not Turning Off?

When radiators fail to turn off, it often indicates an issue with the control system, the radiator itself, or the central heating system. Common reasons include:


Thermostatic Radiator Valve Issues

 If the TRV is stuck, it may not respond to temperature changes. Sometimes, it can be freed by gently turning it back and forth. However, if it’s damaged, replacement is necessary.


Central Heating System Problems

Issues with the boiler or central heating system, such as a malfunctioning pump or an airlock, can affect the radiators. A professional inspection is recommended for these complex problems.


Incorrect Thermostat Settings

The central or room thermostat settings might be too high, causing the radiators to remain on. Check and adjust the thermostat settings accordingly.


Air in the System

Air trapped in the radiator can prevent proper hot water circulation, leading to uneven heating. Bleeding the radiator to release trapped air might resolve this.


Blocked or Dirty Radiator

Sludge or debris in the radiator can impede water flow and heat distribution, requiring cleaning or flushing.


Wiring Issues

Faulty wiring in the heating system’s controls can cause radiators to stay on. This requires an inspection by a qualified electrician or heating engineer.

If basic troubleshooting doesn’t solve the problem, it’s advisable to seek help from a heating engineer. Fixes on complex heating systems can inadvertently cause more harm if not handled properly.


Why is Heating On When It Should Be Off?

There are two main reasons that your heating is on when it should be off. It normally comes down to a problem with either your diverter valve or your check valve. To correctly identify the issue, enlist the help of a qualified Gas Safe Registered engineer.

They’ll run some tests and establish whether it is indeed a check valve or diverter valve at fault – or a different underlying issue altogether. Thereafter, they’ll advise you on the findings and carry out the repair work to restore or clean your central heating system.


Get advice when heating off but radiators on 

Get in touch with a qualified engineer to come and take a look at the problem. 

At JustBoilers.com, our team of experts can assist you when your radiators are on but your heating is off with ease. We can also repair your boilers to ensure your home or business is heated efficiently. Find out other reasons why your radiator might not be working.

Get in touch with an expert to understand why your radiators are hot when the heating is off.