Why is one radiator cold when your heating is on?

An old couple checking the temperature of their radiatorAn old couple checking the temperature of their radiator

If you've switched on your central heating system and discovered that there's a particular radiator that simply won't get hot then it can be very frustrating. The important thing to know is that, while it's inconvenient, it's actually a fairly common issue that is not necessarily a sign of anything too serious. There are a few things you can try yourself that could solve your problem and get that pesky radiator up and running again. We'll run through some of the various options open to you below to help you get the problem of a cold radiator resolved.

Bleed your cold radiator

Throughout the life of a central heating system, there will often be times when air makes its way into the system and gets stuck at the top of a radiator. A symptom of trapped air is a radiator that is hot at the top but cold at the bottom - the air is stopping the hot water from reaching all the way to the top of the radiator and is therefore stopping it from getting up to its full potential.

Letting the air out, or 'bleeding, the radiator will allow the air to escape and the hot water to rise all the way to the top of the radiator, enabling it to get hot evenly.

In order to bleed your radiator:

  • Turn your heating off and allow it to cool down
  • Turn both radiator valves anticlockwise so that they are open
  • Use a radiator bleed key and put it into the radiator bleed valve. Or use a flathead screwdriver
  • Turn the key slowly in an anticlockwise direction by a half turn. You'll hear the hissing of the trapped air escaping
  • Have a cloth ready to catch any drops of water
  • Once the water starts to come out, tighten the bleed valve back up
  • Switch on your heating and see if the radiator now heats up

Check your TRVs

Thermostatic radiator valves are a very important part of a heating system. You set them according to the numbers on the valve, which each correspond to a particular temperature that you would like the room to be at. The thermostatic valves detect the temperature in the room and allow hot water into the radiator when the temperature drops too low. Once the optimal temperature has been reached, the valve automatically shuts off. The valve will constantly be opening and closing as needed in order to maintain your desired temperature.

However, if the valve is old or hasn't been used for a while, the pin inside the valve can get stuck in the closed position. The pin is the component that enables the valve to open and close. A stuck TRV pin is often responsible for a cold radiator.

In order to free a TRV radiator pin:

  • Remove the head/cap from the thermostatic valve
  • Take a pair of grips and grip the exposed pin
  • Gently move the pin up and down until if freely moves
  • Turn your heating on and see if the radiator gets hot

If you can't free up the pin in your old thermostatic radiator valve, it might be worth considering purchasing a new set of valves. Not only will this get your radiator working again, but it may also improve the energy efficiency of your heating system.

Trade Radiators provide an unrivalled selection of radiator valves. No matter what type of radiator installation you have, we’ll have a set to suit your requirements. All our valves come with extensive guarantees and free delivery. You can always get advice on certain maintenance aspects from the team and we try to make sure you can get everything you will need as quickly as possible and help you save money in the process. 

Take a look at our current stock and we’ll help you find the ideal thermostatic radiator valve.

Balance your heating system

When it comes to a fully functioning heating system, it's important that the flow of water is even throughout all your radiators, which is known as a well balanced system. If the water flow is imbalanced then it could be the case that your cold radiator is not receiving the hot water it should be. This is wuite common with a radaitor that is at the extremity of the system (i.e. the furthest radiator from the boiler). Thw hot water maybe flowing through the other radiators but returning back to the boiler before reaching that particular radiator. If that is the case then your system will need re-balancing.

Balancing your radiators is not a difficult task but can be a little time-consuming so it's worth putting an hour or so aside in order to get it don. If you watch the video below, you'll see a professional plumber take you step-by-step through the exact process of rebalancing your radiators which will help you get that cold one hot again.

Regular heating maintenance

If the recommendations above haven't solved the issue, then you should consider calling in a professional plumber or heating engineer to see if the problem is something more serious. They will be able to get to the bottom of the issue and have your radiator running hot again.

Regarless of whether or not you have an issue with your heating, it's recommended to have your boiler and heating system inspected every 12 months. A heating engineer will service your boiler, top up your chemical inhibitor levels and generally ensure your system is running efficiently and smoothly, just like you might take in a car to get serviced.

Annual heating maintenance is the best way to ensure your heating is doing what it should without running up unnecessarily large heating bills and to minimise the chances of a boiler breakdown when you most need it.

12 July 2022