A radiator that stays warm when the heating is turned off can be confusing at first, especially when the rest of the system has cooled down. I’ve had this happen before, and it made me think the boiler was still running even though everything was switched off. Once I looked into it properly, the reason became clearer, and it wasn’t anything dangerous or dramatic, but it did need sorting to get the system working the way it should.
In my situation, the radiator stayed warm because the valve wasn’t closing fully. Even when the heating was off, a small amount of hot water continued to pass through the pipework and into the radiator. TRVs can stick over time, especially if they’re older or haven’t been moved much. When I turned the TRV fully down and then back up a few times, it loosened enough for the flow to stop properly. After that, the radiator cooled at the same pace as the others in the house.
Another time, the issue was caused by heat from the return pipe rather than the radiator itself drawing in new water. The pipework beneath the radiator stayed warm for longer than expected, and the heat transferred into the bottom section of the panel. The radiator wasn’t actually being fed water from the system; it was just absorbing warmth from the surrounding pipe. Once I insulated that part of the pipework, the radiator stopped giving the impression that it was running after the heating had switched off.
There was also a case where the radiator stayed warm for longer because the system wasn’t balanced. Radiators closer to the boiler tend to hold their heat for longer, while those further along cool more quickly. In one of my previous homes, I noticed that the same radiator always seemed to stay warm after everything else had cooled down. When I balanced the system properly, that radiator started heating and cooling at the same pace as the rest. If you haven’t balanced your system before, this guide explains the exact method I used: How to Balance Radiators Properly.
It’s also worth checking the boiler settings. Some boilers have pump overrun features that keep water circulating for a short period after the heating switches off. This is normal, and it’s there to protect the boiler. But if the overrun lasts too long or continues feeding heat into certain radiators, it can make it feel like the system hasn’t turned off. In my case, adjusting the temperature setting on the boiler helped stabilise how long the radiators stayed warm afterwards.
If you’ve recently had pressure issues, that can also influence how long radiators hold heat. When pressure isn’t stable, the water flow becomes unpredictable, and certain radiators behave differently from the rest. Once I dealt with the pressure issue in my own system, the radiators all cooled down evenly again. If that sounds familiar, this guide explains the problem in more detail: Why Your Boiler Keeps Losing Pressure (And the Fixes That Actually Worked for Me).
If the radiator continues to heat when the system is off, even after checking the valves, balancing, and looking at the boiler settings, then the valve may need replacing. A valve that doesn’t close properly will always allow some movement of warm water, even when the heating is off. Once the faulty valve was replaced in my case, the radiator behaved normally again.
If you’re trying to get your whole home to warm and cool more predictably, or if you’ve been working through multiple radiator issues at once, the guide that helped me understand how everything connects is this one: How to Keep a UK Home Warm for Cheap (Complete Guide). It ties all the small heating problems together and helps make sense of the bigger picture.
