fix cold radiators

Cold Radiators – How To Potentially Resolve This Issue

Have you noticed that your radiators never seem to get hot enough? Do some of your radiators have cold spots? Have your radiators completely stopped working?

If so, then you have reached the right place. In this guide, we are going to share the reasons for the most common radiator problems and how they can be resolved, including:

✓ All radiators are cold
✓ A single radiator is cold
✓ Radiator cold at top hot at bottom
✓ Radiator cold at bottom hot at top
✓ Radiators downstairs are cold but hot upstairs (and vice versa)

If you have any questions or need to make a booking, contact Quantum Gas Engineering on 0203 633 2322 or send us an email at

All Radiators Are Cold

When all of your radiators are cold, it usually indicates a system wide problem with the boiler or your central heating plumbing. The very first thing you should do is check that the central heating is switched on and running.

If it has no electrical power
An electrical fault may have occurred which has caused your boiler to shut down. If you experienced a recent power surge or blackout, it could have tripped the boiler’s fuse. Check the boiler control panel to see if the fuse is still operational.

Next, head to your property’s fuse box check for a tripped RCD switch. It would have flicked to the off position. All you need to do is turn it back to ‘on’. If you are using a pay-as-you-go electrical metre, check that you still have enough credit available and that power is actually arriving at your boiler.

If it has electrical power but is not heating
If the boiler still has electrical power, check that the thermostat and timer are set correctly. Someone in your household may have adjusted these settings, leading to the boiler turning off.

If that hasn’t fixed it, look for error codes on the boiler’s display panel. There may be an issue with the water pressure, gas supply, flame settings, flow thermistor, outside sensors and so on. You can deal with some of these issues yourself, but you may require help from a heating engineer to deal with more complex problems.

There may also be an issue with your central heating plumbing, like a leak. If you see any evidence of leaks, contact a plumber or hearing engineer immediately.

In some cases, power cycling the boiler can help. Simply turn it off then back on again. Although the line “Have you tried turning it off and on again” is often considered a joke, it can actually work in some cases.

A Single Radiator Is Cold
If a single radiator is cold, that’s great news, as it means the issue is isolated to that particular radiator. If the radiator is cold all over, start by checking that the valves on both sides of the radiator are open. If they are not, hot water will not be able to successfully flow through the radiant, impairing its performance.

If the valves are open, there could be a blockage preventing hot water from reaching the radiator. Limescale and sludge can sometimes cause blockages in specific radiator pipes. Fixing this issue involves removing the radiator and flushing it.

Radiator Cold At Top Hot At Bottom
When a radiator is cold at the top but warm at the bottom it usually indicates that there is air trapped in the radiator. The air prevents the warm water from reaching the top of the radiator, leading to a large cool spot which impairs its performance.

Fortunately, it is simple to fix this issue. You will need to bleed the radiator to remove the air trapped inside. To do so, follow these steps:
1. Turn off the heating system
Turn off the boiler, so the water can cool down slightly
2. Identify the type of radiator bleed valve you have
The bleed valve will be near the top of the radiator. Some radiators will require a special radiator key to turn this valve while others will need a flat head screwdriver. Hardware shops sell radiator keys if you need one
3. Get ready for clean up
Some water may escape the radiator when you bleed it, so grab a few towels to mop it up.
4. Undo the valve
Use the key or screwdriver to slowly turn the valve anti-clockwise. You will hear a hissing sound, which is the air escaping from the radiator
5. Keep the valve open until all the air is out
When water begins to exit the radiator, you will have successfully finished bleeding it.
6. Close the valve
Job done, great work.

If require any assistance bleeding your radiators, contact a heating engineer or plumber.

Radiator Cold At Bottom Hot At Top
This symptom usually indicates that there is a build up of sludge in the bottom of your radiator. This is a little tricker to deal with, as the radiator needs to be removed from the wall and cleaned out. It can be a messy job and one that most homeowners prefer to outsource to a specialist.

Sludge remover can also be added to your central heating system, which does a decent job of dealing with small amounts of sludge. If several radiators are experiencing this issue, you may benefit from having a power flush performed by a heating engineer. This process will remove all of the sludge in your heating system, which can greatly improve its performance.

Radiators Downstairs Are Cold But Hot Upstairs
If you have a multi-level property and discover that radiators on one floor are colder, it can indicate that there is an issue with your heating system’s central pump. the pump may be struggling to send hot water throughout the entire system.

In some cases, you may be able to fix this issue yourself. If you have a pump that is stuck, gently tapping it with a hammer can free it up. However, if you notice that the pump is very noisy, hot, or rattling, then it is probably past its used by date and needs to be replaced.

Another possible cause of loss of heating on one floor is insufficient water in the expansion cistern. This cistern is typically located in the loft and and is responsible for supplying additional water in the system.

Check it by lowering the float arm valve manually. If the tank does not refill with water, then there may be an issue with the float valve. If manually refilling the tank does temporarily fix the problem, it indicates that there is an issue with the cistern’s water levels and a heating engineer needs to take a look.

Thanks for reading. If you have any questions or need to make a booking, contact Quantum Gas Engineering on 0203 633 2322 or send us an email at

Quantum Gas Engineering Ltd. Are Accredited Viessmann installers.

Interested In Learning More? Contact Quantum Gas Engineering

For more information on Vaillant boiler installations in Primrose Hill, give Quantum Gas Engineering Ltd a call on 0203 633 2322 or email us at