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Central Heating Flushing

Central heating is one of the most energy efficient and cost-effective forms of heating available in the UK today. However, over time any central heating system can become blocked with sludge, rust, and debris, which will make it much less efficient.

If the central heating struggles to fully heat the house, or fuel bills become excessive, it may be necessary to flush the heating system and clear any blockages to make sure it is operating effectively. Equally, if you are having a new boiler fitted, it is usually recommended to have the heating system flushed in advance.

Modern boilers have more compact heat exchangers which can be prone to problems caused by sludge and debris in the circuit. Some manufacturers insist that you power flush central heating before installing one of their boilers.


How to power flush a central heating system

Power flushing central heating involves pumping a mixture of cleaning chemicals and water around the central heating circuit to clear out the debris.

If less efficient, central heating systems may need flushing through to remove sludge and debris.

Older central heating systems may need flushing through, to remove sludge, rust and debris.

The pump used to power flush a system operates at a much higher flow rate than a typical central heating pump; and the combination of a high flow rate and the cleaning agents helps to clear limescale and corrosion from the internal surfaces of the radiators and the pipe work.

The flushing pump is fitted into the heating circuit wherever is most practical, and cleaning chemicals are flushed through the entire system. The rust and debris will loosen from surfaces and become suspended in the flow of water and cleansing chemicals.

Each radiator can be flushed independently from the system by closing other valves and concentrating the flow from the pump through each radiator individually. When finished, the system will be purged with clean water, and the dirty water and debris will be drained off.

Although a central heating power flush operates at a high flow rate, it is not a high pressure system; so it can be done in your home while the system is in situ, often without the need to remove radiators or the boiler.


Why flush your system?

There are several reasons that may require you to flush your central heating, and a variety of tell-tale signs to look out for. If the system becomes particularly slow to heat up or you notice cold spots on radiators, or radiators that fail to heat at all, then the system may well need flushing.

If radiators need to be bled frequently and the water contains black sludge, this is another indication that the central heating needs to be flushed. Other things to look out for include excessive noise from the boiler, or continual pump failures.


The benefits of flushing your central heating

Central heating flushing will restore the system to as near as possible to maximum efficiency. Problems with flow and circulation should be cured and the entire system will be cleaned, including radiators and underfloor pipes.

Without obstructions and blockages, the boiler can work much more efficiently to produce the maximum heat output, and radiators will emit the full amount of heat. You can also expect to see a noticeable difference in your energy bills, as the system will burn much less fuel to achieve the same level of heat as before the flush.


The costs

The cost of having a central heating system flushed depends on the size of the house, the amount of radiators in the system, and the quantity of chemicals required for the job.

On average you could expect to pay around £35 – £40 per radiator for a system flush, although costs could be higher if the boiler or radiators need to be uninstalled.

It is also possible that a system flush could expose very high levels of corrosion within radiators, resulting in leaks once the flushing is completed; there is no other option but to replace the radiators.

There is no way of carrying out an internal inspection prior to a flush, but if corrosion has reached such a point, a leak would develop eventually; so it is better to find out during a flush when the radiator can be quickly isolated.

Cost of flushing central heating systems is dependant on size of house and number of radiators in the system.

The cost of having a central heating system flushed, depends on the size of the house and the amount of radiators in the system.


Problems with flushing central heating

If a system is very old, or has not been serviced for a long period of time, there is likely to be severe debris, sludge and corrosion within the boiler, radiators, and pipe work.

A full system flush may not be able to completely clear the system, and radiators may still suffer from cold spots, or fail to heat. If this is the case in your property, it may be worth considering upgrading the entire heating system rather than going to the expense of having it flushed.

Microbore systems are not always as effectively treated by flushing as larger bore systems. Microbore pipe work is usually 8-10mm, and because of the smaller diameter, the flow rate of the flushing pump is reduced and less debris and sludge can be cleared.



Central heating systems need to be maintained correctly to achieve maximum efficiency. One of the greatest advantages of central heating is lower fuel bills, and with energy prices ever rising, it is important to reduce energy usage as much as possible.

Running an old or severely blocked central heating system will not only leave your house cold and uncomfortable, but also add a significant amount to your heating bill through wasted energy.

A central heating flush will clean out all the rust, debris and sludge that can build up over time and block the system, and restore your heating to near maximum efficiency. A flush works by connecting a high flow-rate pump to the circuit, and pumping a mix of water and cleaning agents through the system.

The high flow rate and turbulence through the pipe work helps to loosen debris from internal surfaces, and the system can then be drained and purged with clean water. Although a full system flush can be quite expensive, estimates suggest it could save between 10% – 20% on heating bills, depending on the severity of the problem.

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