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Why is my radiator cold?

Common reasons why radiators are not working

If your radiators feel cold or they’re not heating up as they should or have done, you’ll want to know why. While cold radiators could be a result of a more serious problem with your central heating system or boiler, there are a number of other more minor issues that should be checked out first.

Diagnosing your radiator problems

It can be confusing and frustrating when there are cold spots on radiators, particularly when you’re trying to get a room nice and cosy. There are a few things that can cause cold spots in radiators. Here’s a list of the most common causes to check out when you first discover your radiator is cold or has a cold patch:

  • Your room thermostat is set too low
  • Your timer isn’t working or isn’t set to ON
  • The radiator valve is closed
  • There is air in the radiator
  • There may be a blockage within the radiator
  • There could be a circulation fault

Why are some of my radiators not working?

If none of your radiators are heating up properly then there could be a problem with your central heating system, pump or boiler. However, if some of your radiators are heating up while others aren’t, this could be one of a number of issues. If you are unsure of the issue, seek help from your heating engineer.

Cold radiators in some parts of the home

If a radiator in your home isn’t getting hot, it may be due to a problem with one of the zones in your central heating system.

Central heating systems work by pumping a continuous flow of hot-water from the boiler to the radiators, then back to the boiler to pick up more heat. Within this system, you could have seperate ‘zones.’ This means that you can control the temperature in separate areas of your home, depending on your heating requirements in each room. If you find that radiators are cold in one area, it could indicate that there is a problem with that particular zone.

One radiator not working

If you find that only one radiator within your home stays cold, ensure that the valves located on the sides of the radiator are open. You can check this by ensuring if you have manual valves that they are turned fully anti clockwise or/and if you have a thermostatic valve the other end, again fully turn anti clockwise. If the valves are open but the radiator is still cold, it’s possible that the valves are blocked. A suitable system cleanse conducted by a Gas Safe Registered engineer will usually do the trick.

Cold radiators upstairs

If the upstairs radiators in your home are cold, it could be that the feed and expansion tank in your loft has run dry. This usually points to a larger problem. However, it’s also possible that the ball valve in the tank isn’t working correctly; it may be blocked or jammed.

Try the following:

  1. The cistern is usually found in the loft
  2. Clear any obstructions to the ball valve
  3. Refill the cistern, but only to half way to make sure there is still enough room for the water to expand when the system heats up


When the system is cold there should be just enough water to make the ball float and switch off the water coming in


It’s highly recommended that you seek the skills of a Gas Safe registered engineer when you have major heating or boiler problems. Remember that all boilers and heating systems should be regularly checked and serviced by a competent engineer.


With a full cistern you will then need to bleed your upstairs radiators (make sure your system is switched off first) Once you have bled your radiators switch the system back on and the upstairs radiators should start heating, but it’s a good idea to get a professional plumber in to work out why the cistern ran dry in the first place.

Cold radiators downstairs

If your downstairs radiators are failing to heat up, there could be a problem with your pump. If this is the case, it won’t be producing enough power to push the water around the heating system.

Pumps can get warm, but if it is hot or making a grating sound, then it might be about to break down, in which case it will need replacing. One of our Gas Safe registered engineers can provide help and advice to rectify this issue.

Why is the top of the radiator cold?

If the top of your radiator is cold, it’s possible that air is trapped within the system. Bleeding the radiator will release any trapped air, vastly improving the efficiency of your entire heating system.

Why is the middle of the radiator cold?

If the middle of your radiator is cold, there may be a build-up of debris or sludge which is obstructing parts of the bottom of the radiator. You’ll need to clean it out and remove all unwanted substances that are blocking the bottom length of the radiator.

If you have an open-vent system:

  1. Buy a heating system sludge remover at your local DIY store and use as per the manufacturer’s instructions
  2. Partially drain your heating system
  3. Add the liquid to the feed and expansion tank and refill and bleed the radiators.
  4. After a few days you will need to empty and refill the system.

If you have a pressurised system:

  • You’ll need a plumber or heating engineer to help you
  • They will remove the radiator and flush it out to clean it
  • In some cases, your radiator will need replacing

Why is the bottom of the radiator cold?

If your radiator is hot at the top but cold at the bottom, there may be a build-up of scale, rust, or sludge which is obstructing the flow of water.

As with the middle of the radiator, if you have an open-vent system which is unpressurised and tank fed, you’ll be able to use a sludge remover to flush your radiator. However, if you have a pressurised system, you’ll need the assistance of a Gas Safe registered engineer.


If you’re still stumped as to why your radiators aren’t working, our expert engineers will get things working again in no time.


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