Diagnose central heating problems

If you suspect there's something wrong with your central heating then our handy tips may be able to help you get things back on track. You may also find our tips on common boiler problems useful too.


Cold radiators

There are a number of reasons that might cause your radiators to be cold. It may sound obvious, but first check that you have turned your heating on. Cold radiators could also mean a simple fuse has blown on your boiler, and in the worst case scenario indicate complete boiler failure.

Here are our handy tips that will help you diagnose common central heating problems:

The top of my radiator is cold

This probably means there's air in the system. You will need to bleed the radiator so that this trapped air can be released.

The centre or bottom of my radiator is cold

This may mean a build up of limescale, rust or sludge is obstructing the flow of water.

Build-up of rust and sludge

The method of solving this problem will depend on whether you have an open vented system or not.

  • I have an open vent system
    If you have an open vented system, you can use a heating system sludge remover. This can be bought at most DIY stores. Add the liquid to the feed and expansion tank. After a few days you will need to empty and refill the system.
  • I don't have an open vent system
    If you don't have an open vent system, you'll need to flush through the radiators with a hosepipe. See your manufacturer's manual for instructions on how to do this.

Cleaning your heating system can be a big job, if in doubt get a professional plumber out.

Cold radiators upstairs

Cold radiators located in the upstairs section of your home usually mean that the feed and expansion cistern is empty.

  • The cistern is usually found in the loft.
  • Refill the cistern so that there is just enough water to float the ballcock.
  • Don't fill it up completely, as there must be enough room for the water to expand.

With a full cistern the upstairs radiators should start heating, but it is 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 then there's a good chance that your pump is broken or on its way out. You'll need to call on the skills of an expert plumber.

Remember, cold radiators could lead to frozen or burst pipes in winter, so they need to be tackled quickly.

Air pocket system

In some cases it's likely there’s air in the system and not just an individual radiator. You can tell when this is happening because your radiators will go cold alternately as air pockets move around the heating system. Try bleeding the radiators first before getting in professional help.

Close the valve

Radiators heat up in turn, which means those nearest the boiler will often be warmer. By partially closing the lockshield valve on those radiators you can allow more hot water to flow to the ones further away.

Use a radiator thermometer

Ideally, you need to use radiator thermometers and adjust each radiator in the order in which they heat up. Turn off the lockshield valve, place a thermometer at either end of the radiator and open the valve slowly until the temperature at either end is almost the same.

Leaking radiators and pipes

When you have one or more leaking radiators, there are some actions you can take before the problem escalates. A pinhole leak on a radiator can be a sign of internal corrosion. This can happen when debris that collect during installation aren’t properly removed (and this can be within weeks of a system being fitted) or because of air being drawn into the system.

To fix the problem, try the following:

  • Shut off your boiler and let it cool. As the system cools, water will flow back out of the radiator to the boiler, so it isn't necessary to shut off the water.
  • Turn off the valves at each end of the radiator to relieve pressure.
  • Remove the radiator and leave the rest of the system running. Your manufacturer's manual should contain detailed instructions on how to do this. If in doubt get a professional plumber out.
  • Flush out the system using a non-acidic cleaner.
  • Refit the radiator.
  • Leaky connection or joint
    If water is leaking from a connection or joint then it should be easy to tighten the joint with a spanner or wrench. However if the joint has been soldered you won't be able to tighten it and the pipe may need replacing.
  • Leaking from a pipe
    If a pipe is leaking from a section which has no joint or connection, the pipe will need replacing. A short-term solution is to tie a rag around the pipe, or use specialist sealant from a DIY store. You may wish to get a professional plumber to replace the pipe as it can be a messy and complex job.

Water gurgling

Water gurgling noisily through the central heating system is a clear sign that you have air in the radiators. This problem can be easily resolved by bleeding your radiators.

Don't forget

If you have a major problem with your boiler or heating, call in a Gas Safe Register approved heating engineer. Remember that all boilers and heating systems should be regularly checked and serviced by a professional.

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