Ensuring that your home is sufficiently heated is an absolute must.

During the colder months, a well-heated home is not only crucial for your comfort and health, but it’s also important for your bank balance too.

But, if you’re having problems with the cold radiator and you can’t seem to heat your whole home, then you could be in for a long winter.

This guide will cover the following:

Radiator quick fixes

Fortunately, if you are suffering from radiator problems, there are a range of quick fixes that can rapidly improve the heating in your home.

These include:

  • Bleed the radiator
  • Restart your central heating pump
  • Reset or replace the thermostat
  • Turn on the manual control valve
  • Reset the lockshield valve
  • Clean sediment and debris out of the inlet or outlets

Now, if you’re new to fixing cold radiators, this is where things can start to get a little complicated.

That’s why we’ve created this complete guide to fixing central heating radiator problems. Taking you from bleeding a radiator to fitting a central heating pump, this guide will help you improve the heating in your home.

How does a radiator work

First, before you grab your tools, it’s important that you know how a radiator actually works.

In a central heating system, a condensing boiler heats water before pumping the water around a circuit of pipes in your home. Each of these pipes will run through a radiator as well as underfloor heating. The amount of water that flows through your radiator will depend on the radiator valves settings. The higher the valve setting, the more water that can run through your radiator. After the water has passed through the radiator, the water will be piped back to the boiler.

  • Step 1: Water is heated in a condensing boiler
  • Step 2: The water is pumped around a circuit of pipes
  • Step 3: The hot water enters the radiator
  • Step 4: The water exits the radiator
  • Step 5: The water then cools before returning to the boiler
graphic showing how a radiator works

In a well-designed plumbing system, a radiator circuit will be split into several small circuits (rather than one large circuit) to ensure all radiators are equally heated.

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My radiator is cold at the top and hot at the bottom

If your radiator is cold at the top and hot at the bottom, then you can almost guarantee that there is trapped air in the system. To solve this problem, you will need to bleed the problem radiator.

graphic showing the radiator is cold at the top and hot at the bottom

Warning: Never bleed radiators when they are hot. Scalding water could be released.

Tools needed:

  • A cloth
  • A radiator bleed key or a flat-head screwdriver
  • Step 1: Ensure that your central heating is turned off. Allow time for the radiators to cool down.
  • Step 2: When the radiators are cool, and starting on the downstairs radiators first, take the radiator bleed key and slowly turn the bleed valves anti-clockwise in the top corner.
  • Step 3: As you’re turning the valves, place a cloth under the valve and prepare for a trickle of water to escape. At this point, you should be able to hear the sound of trapped air escaping from the radiator. Stop turning the valve and allow the air to escape.
  • Step 4: After the sound of air escaping subsides, turn the valve clockwise and tighten.

Note: Remember to bleed all the radiators in your home.

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All my radiators are cold

Unfortunately, if all the radiators in your home are running cold, then you could have a variety of different problems. The first thing to check is your boiler pressure. If the boiler has stopped working, then you will need to call a central heating engineer. If the boiler pressure is still running, and you’re still getting hot water at the taps, then you could have a variety of problems.

These include:

  • The central heating pump is turned off or faulty
  • Thermostat or timer is incorrectly set or faulty

Problem: The central heating pump is turned off or faulty

If you have more than one radiator not working or all of your radiators are running cold, and you’ve checked that the boiler is working, then your central heating pump could be faulty. A central heating pump is a small mechanical tool installed on your central heating system, which is used to speed up the process of circulating hot water from your boiler to your radiators, underfloor heating, and back to the boiler. If the pump is turned off or faulty, then the hot water will not be able to reach the radiators before cooling down.

Solution:The first thing you need to do is shut down the boiler

You will then need to do an inspection of the pump. Is it running? Is there any damage to the pump? Is the pump casing vibrating? If everything seems fine, then turn off the pump at the mains. Now check all the wiring connections. Sometimes the wires can come loose causing the pump to shut down.

You can read our alternative guide if you want to learn more about fixing central heating pumps.

Problem: Thermostat or timer is incorrectly set or faulty

One of the biggest radiator problems relates to the thermostat not working correctly. These devices regulate temperature and can either stop working altogether or can work intermittently, shutting themselves off at random intervals.

Solution: Call an engineer to fix the thermostat

If the boiler and central heating pump are working, then it could be a faulty thermostat. A faulty thermostat could be caused by a variety of factors. These include:

  • The thermostat is placed in an area with a draught
  • The thermostat is placed near a heat source
  • Faulty wiring and connections

Try resetting the thermostat or fiddling with the wiring connections. If this does not solve the issue, then you will need to have a thermostat inspection conducted by an engineer.

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Some of my radiators are cold

If only a few of your radiators are cold, then it’s likely your central heating pump is faulty or broken. If the central heating pump is still working, then you could have any of the following problems.

These include:

  • The zone valve thermostat or timer is incorrectly set or faulty
  • The system is unbalanced
  • The zone valve is faulty

Problem: The zone valve thermostat or timer is incorrectly set or faulty

There will be multiple thermostats distributed in different areas of the home. These thermostats will connect to different zone valves on your radiators and will pump hot water to your radiator as and when needed. A faulty thermostat will not allow the zone valve to operate correctly causing some radiators to run cold while other radiators run hot.

Solution: Call an engineer to fix the thermostat

Unfortunately, if you have a faulty thermostat, then there’s not a lot you can do. A faulty thermostat could be caused by a variety of factors. These include:

  • The thermostat is placed in an area with a draught
  • The thermostat is placed near a heat source
  • Faulty wiring and connections

Try resetting the thermostat or fiddling with the wiring connections. If this does not solve the issue, then you will need to have a thermostat inspection conducted by an engineer.

Problem: The system is unbalanced

Balancing the radiators means adjusting the radiator valves so that all radiators heat up at the same rate. If a radiator is too cool, it needs more hot water. If a radiator is too hot, then the water needs restricting. A system is balanced by using the “lockshield” valve to increase or decrease the amount of water a radiator receives.

Solution: Call an engineer to balance the system

Unfortunately, if your system is unbalanced you will need an engineer to conduct the rebalancing. Balancing a system needs technical equipment like a digital thermometer or multimeter and needs to be conducted by an experienced professional.

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One of my radiators is cold

If only one of your radiators is cold, then it’s likely your central heating pump is faulty or broken. You can read our complete guide to fixing a central heating pump here. If the central heating pump is still working, then you could have any of the following problems.

These include:

  • The radiator’s manual control valve is turned off
  • The thermostatic radiator valve (TRV) is set incorrectly or faulty
  • The lockshield valve is set incorrectly
  • Debris is blocking the inlet and outlet

Problem: The radiator’s manual control valve is turned off

Radiators can have two different types of valves. These are a thermostatic radiator valve and a manual valve. The manual valves are effectively the same as taps. You turn the valve to control the temperature. The more you turn the valve, the more hot water the radiator receives.

Solution: Open the valve

Problem: The thermostatic radiator valve (TRV) is set incorrectly or faulty

Radiators can have two different types of valves. These are a thermostatic radiator valve (TRV) and a manual valve. The thermostatic radiator valve (TRV) has an inbuilt temperature sensor which keeps the room at a constant temperature. If the thermostatic radiator valve is set incorrectly or faulty then the radiator may not turn on.

Solution: Reset it or contact an engineer

Try resetting the thermostatic radiator valve. If this doesn’t solve the problem you may need to contact an engineer.

Problem: The lockshield valve is set incorrectly

The lockshield valve is the valve on a radiator that is usually covered with a plastic cap. This valve is used when balancing the system. If the lockshield valve is set incorrectly it may restrict the necessary amount of water from reaching the radiator.

Solution: Adjust the lockshield

First, turn the manual or thermostatic radiator valve to full. After thirty minutes, use an adjustable wrench to slowly open the valve. When the radiator starts to warm up stop turning. You will now need an engineer to rebalance your system in the future.

Problem: Debris is blocking the inlet and outlet

As the radiators age, the inlets, pipes and outlets can start to corrode and rust. This causes a build-up of rust in the inlet restricting water from reaching the radiator.

Solution: Flush the problem radiator

You will need to remove the radiator from the wall and flush the inside of the radiator. See the flushing instructions below.

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My radiator has a cold centre

Problem: A build-up of sludge

If the radiator has a cold centre or is cold at the bottom, then it’s likely that you have a build-up of sludge. This is where air, water and debris mix inside the radiator and restrict the flow of water.

Solution: Flush the radiator

Warning: Never flush a radiator when hot. Scalding water could be released.

What tools do you need?

  • Plastic sheet
  • Radiator key
  • Two adjustable wrenches
  • Bucket or bowl
  • PTFE tape
  • Hosepipe and water supply

Step 1: Turn off the heating
Ensure the heating is turned off. Leave the system for at least three hours to cool down.

Step 2: Lay out a plastic sheet
Lay out a plastic sheet to catch any sludge, debris or water

Step 3: Turn off the thermostatic valve
Twist the valves to “0” or “off”

Step 4: Shut off the lockshield
Use the wrench to twist the lockshield clockwise to shut off the water

Step 5: Open the air bleed valve
Remove any air from the radiator by opening the bleed valve

Step 6: Shut the bleed valve
After the air has escaped (the hissing has stopped), shut off the bleed valves

Step 7: Slacken the radiator valve
Use a pair of grips and an adjustable spanner to slacken the radiator valve. Drain the radiator water into the bucket. Do this until the radiator is empty.

Slep 8: Remove the radiator valves
After the radiator has emptied, remove the radiator valves and take the radiator outside

Step 9: Flush the inside of the radiator using a hose
Insert a hose inside the radiator and flush the inside until clear

Step 10: Flush from the other end
Flush the radiator from both sides

Step 11: Place the radiator back on the wall
Once the water is running clear you can put the radiator back on the wall. Remember to open up the radiator valve and top up on any pressure loss. Turn on the heating system.

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Free Advice

If you’re struggling for advice, ring our dedicated pump experts for free advice on 0800 112 3134 or 0333 577 3134. We’re open Monday to Friday 07:00 - 17:30 and Saturday 08:30 - 12:30.