Radiator Won’t Turn Off? Here’s Why

If your radiator won’t turn off, there are a few things that could be causing the issue. Trust me – we don’t want to get this fixed as bad as you do, but only barely. I know from personal experience how miserable a home with nonstop radiators can be, and wouldn’t wish it on my worst enemy. Okay, maybe on one enemy, but not on most of them. Wait… I’m being told that most people don’t have enemies – is that true? I’m getting a bit off target here, so let’s just dive right in.

If your radiator won’t turn off, it’s likely because of a bad check valve, thermostat problems, or issues with your diverter.

Let’s break that down a bit more, shall we?

Radiator Won’t Turn Off: Causes

Now there are three major causes of a radiator that just won’t stop heating. The first, most likely one is that there’s something wrong with your thermostat. However, there are also internal bits that could have broken or just lived their lifespan and are ready to retire.

Read Next: Worcester boiler – no green light (solved).

Check Valve

This is more common in older homes with a boiler that always is heating water. This hot water rises and travels through convection to your radiators. When the heat is turned on, a pump pulls water from the boiler and brings it right to the radiators.

Now, theoretically, the pump should shut off when the desired temperature is reached. A check valve prevents convection from bringing any more hot water to the radiator, but if that goes out, it won’t stop. A spring or weight generally keeps the check valve closed, and consequently, that’s the part that usually fails.

If your check valve is dirty, has mineral buildup, or has broken, it won’t prevent hot water from coming to the radiator. Realistically, the best bet you have here is to call a plumber to take a look. They will be able to figure out if it’s just a cleaning that’s needed, or if a full replacement is necessary.

Diverter Valve

The diverter valve in your radiator is what interacts with your home’s thermostat. We’ll take a look at that in a moment, but first, let’s talk about diverter valves.

Your radiator’s diverter valve is what, well, diverts hot water when needed to the radiator. If both multiple thermostats call for hot water at once, it’ll open into a mid-position, allowing water to all needed areas.

If your diverter gets clogged or stuck open, then there’s likely hot water constantly being delivered to the radiator. To fix this, you can give the valve a good cleaning. If that fails, you’ll need to call a plumber to take a look and ensure it’s replaced and in good condition.

A good way to see if your diverter valve is the issue is to try and run hot water elsewhere in your home. Turn on some taps or a shower on max heat and wait. If the diverter is stuck open, hot water will only go to your radiator. You won’t have hot showers for a day or two, but at least you found the issue, right?

To clean a diverter valve, you can purchase specialised boiler cleaners. Be sure to use the proper one, though, as using the wrong cleaner could have very bad results. It’s best to check with a plumber before dedicating to a particular cleaner, just to be safe.


This is perhaps the most obvious solution. Thermostats are what directly control the temperature in your home. While it’s entirely possible that someone just bumped the thermostat up to max heat, I’m willing to bet you’ve already checked that. If not – go double-check! If that was the issue the whole time, it would be rather embarrassing to call in a plumber, only for them to just… turn down the heat.

The more likely solution is that your thermostat has failed. If you have a mechanical thermostat, you can ensure that it’s getting power and make sure everything inside is functioning. If not, you’ll have to replace the thermostat.

On the other hand, though, we have digital thermostats. These are a bit trickier to troubleshoot, as they have circuit boards and software issues to potentially address. The first thing you should do is ensure that you have live batteries in the thermostat. Next, see if a change in temperature affects any of your heating systems. If it does, the thermostat isn’t the problem. If it doesn’t, consider a hard reset.

This varies on the model, but your owner’s manual generally instructs on how to perform a hard reset. This will usually fix any software-related issues and will rule out the thermostat as the source of the problem.

Finally, if you’re in an old home – double-check that you actually have a thermostat. Some older radiator systems don’t have a master control, which can lead to exactly this issue when you’re not aware of it.

Final Thoughts

While there are a lot of things that could make it so a radiator won’t turn off, the most common sources of the issue are the diverter and check valves and the thermostat. While there are things you can do to pinpoint the issue, it’s often best left to the professionals. IF you’re not the type to ask for help, though, then there are a few things to do.

Check that you have hot water in your taps – if not, it’s likely your diverter valve. If your check valve is old, it’s possible that it’s finally failed (or even dirty). Commercial cleaners are available that you can use to address a dirty check valve, but be sure to get the right one! You can also ensure that your thermostat (should you have one) is powered and working with other parts of the home. Turn it down and see if your radiator or boiler respond. If not, perform a hard reset and if that doesn’t resolve the issue, call a professional. You may need to replace the thermostat, the diverter valve, or the check valve (if not all of them), and a plumber will make it as easy as possible on you.