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Central Heating Problems

There are several problems that you may encounter with a central heating system and it is not always easy to diagnose the cause of the fault.

In some cases it will be necessary to enlist the services of a professional plumber or heating engineer, but many of the problems can be dealt with simply by adjusting the settings, or for the more confident, by embarking on a little bit of DIY.

Some of the more common central heating problems and solutions are listed below, but as always, it is best to consult a professional if you are unsure about trying to repair the system yourself.


You may have to call in help to diagnose problems with central heating.

It isn't always easy to diagnose problems with central heating and you may have to call in help.


The radiators can highlight a variety of different problems, and are usually the first thing you notice about a faulty central heating system.


Cold at the top only

If the radiators are warmer at the bottom but almost completely cold at the top, it is often a sign that the radiator needs to be bled. When air gets into the system it collects at the top of the radiators and prevents the water from heating the radiator fully. You should have a radiator key which opens the bleed valves on the radiators to allow the air to escape and the system to refill with water.


Cold at the bottom only

If the reverse is true and the radiators are colder at the bottom, it is a more serious problem. This could indicate that the radiators are full of sludge and debris, which has collected lower down. The only way to deal with this is by flushing the system with chemicals to clear the sludge; unfortunately this is quite an expensive process.


Cold downstairs but warm upstairs

If the heating appears to be working upstairs but suddenly fails to heat the downstairs radiators, it could point to a problem with the pump. If it is unable to properly circulate the water, a pump can usually be replaced without the need to drain the system.


A single cold radiator

If there is just one problem radiator in a system, which does not heat, it could be that the inlet valve has been closed, and you should check that it is open. It may also point to a failed thermostatic valve, which will require the draining of the system to be replaced.



The boiler is the heart of the central heating system, and any problems will affect both heating and hot water. If you have gas central heating problems, bear in mind that any work to the boiler should be carried out by a gas safe registered engineer.

A gas registered engineer should carry out any work needed on a central heating boiler.

Any work required on a central heating boiler should be carried out by a gas safe engineer.


Boiler cycling on and off but water is only luke warm

If the boiler is turning on and off, but the water is not being fully heated there could be a problem with the flue fan.

If the thermal cut out on the fan is faulty it will cut the gas supply and switch the boiler off at a much lower temperature than it should.

This is one of the reasons for this type of fault, but there could be several others, and it is a job best left to a qualified technician.


Pilot light frequently going out

If the pilot light appears smaller than usual or continually goes out, it might be down to a blockage in the pilot light gas tube, or a failure of the sensors which detect when the pilot light is lit. Again, as the repair will require the removal of the boiler case, it is not something you should undertake yourself.


Unusual noises from the boiler

If you hear unusual or excessive noise from the boiler, it may be blocked by a build up of rust, sludge and debris. This could point to a need to flush the heating system to clean out the heat exchanger in the boiler, as well as the radiators and the pipes.


Leaking central heating pipes

Leaking pipes can often go long periods unnoticed, particularly if they are under the floor, and can cause a good deal of damage. To replace a length of pipe or a leaking connection, the water should be isolated and the whole system should be drained, so you can get to the part and replace it.


Power flushing

Over the course of time all central heating systems suffer from an internal build up of sludge, rust and debris, which can become attached to surfaces and block the circulation of the water. The best solution to this is to power flush the entire system, remove the substances and replace the water.

To do this, a high flow rate pump is connected to the system, and a mix of water and chemical cleaning agents is pumped around the network of pipes and radiators. The velocity of the water, along with the chemicals, frees debris from surfaces and it is carried away when the cleaning fluid is drained off.



Before calling in a plumber it is worth a few simple checks to make sure the problem isn’t something you can easily take care of yourself. Check the times on the programmer to make sure they haven’t been changed or reset by a power cut.

Check the thermostat on the boiler and the room thermostat if you have a problem with the heating; and check the thermostat on the hot water cylinder if there is a problem with the water heating.



Central heating is one of the most popular forms of heating as it is one of the cheapest and most energy efficient. Fortunately, central heating systems tend to be very reliable and do not fail very often. If you do have problems with the heating, it is worth taking the time to try and diagnose the fault yourself before calling in a professional.

If it is just a case of adjusting a few settings, you can save yourself paying the call out fee. If the problem is related to a gas boiler, however, you should contact a gas safe registered engineer immediately to make sure it is dealt with swiftly and safely

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