The Cost to Power Flush a Central Heating System

All you need to know about the costs of power flushing your central heating system including materials, labour and time frames.

Power Flushing

What the job entails

This article is all about power flushing a central heating system and part of our series into the costs charged by gas engineers and plumbers. Power flushing is a technique used to clear any sludge from central heating system from the pipes, radiators and heat exchangers. Where sludge collects scale and corrosion surely follow, the symptoms of a central heating system which needs cleaning out include cold spots on radiators that persist even after bleeding, long warm up times, excessive noise and general inefficiency. But once you carry out a power flush you can expect the pipes and radiators to get hotter quicker, with less stress on the boiler and heat be distributed more evenly throughout the home.

Excessive sludge in the system can cause central heating boilers to fail early, the latest efficient condensing boilers in particular are really sensitive so it’s highly recommended to do a full central heating system power flush before installing a new boiler. There is no point in paying for an expensive new boiler that will end up failing early due to excessive sludge, any savings made due to the more modern and efficient boiler will be lost due to the shortened life and replacement cost. In addition, many boiler manufacturers will not honour claims on any new boiler if the system hasn’t been recently power flushed.

Before commencing with the actual job your plumber will start by firing up the boiler and checking the radiators for any cold spots by taking the temperature of each radiator. Then once all the radiator valves are removed or opened and dust sheets placed over carpets and furniture for protection, the power flushing machine can be connected. The first flush is usually a chemical power flush of the entire system which takes around 20 minutes. Afterwards, each individual radiator is then isolated and flushed while a rubber mallet is used to help loosen up any sludge inside.

The second flush again cleans all radiators individually and the fluid is reversed back and forth until the water is clear on all radiators. Usually a final full central heating system flush is then undertaken until the water is free of any sludge. The final step is to add an inhibitor and circulate it through the system, before refitting the radiator valves.

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Cost to Power Flush a Central Heating System

The average cost to power flush your central heating system is typically around £300-£400 with the price depending on a few factors, such as the number of radiators in your house, your location and whether or not you hire a small or large company.

The typical heating engineer will often charge around £150-£200 a day in labour costs. To flush your system it shouldn't take the tradesman any longer than a day but this will depend on the amount of work that's required, so in some cases it can take up to 2 days.

Below are some estimated costs of hiring a tradesmen to power flush a central heating system:

Number of Radiators Avg. Cost Duration
4-6 £300 1 day
7-10 £400 1 day
11-15 £500 1-2 days

Cost Breakdown

Individual costs for hiring a tradesman to power flush a system in a semi-detached house with 8 radiators - Total Cost: £400






Waste Removal


We would advise homeowners to have a central heating system power flush carried out if a new boiler is being installed or if the system hasn’t been cleaned for a long time. Although the flush will cost around £400, the central heating system will run more efficiently and the house will be warmer with lower fuel bills. This price assumes that the level of sludge is not excessive and the removal of individual radiators is not required.
The time taken really depends on how many radiators there are and also how much sludge or dirt is in the system. But for a typical 3-bedroom semi-detached house assume around 5 hours in total. Though in some cases individual radiators will need to be removed and manually cleaned with a high powered pressure washer due compacted sludge. This will obviously take much longer and will reflect in the overall cost.
No, sludge caught in the radiators will not circulate so won’t be caught in the magnetic filter. These aftermarket filters only catch loose sludge and are regarded by most plumbers as a gimmick.
If flushed by a professional and done correctly then you shouldn’t need to have the system flushed again for 10 years or so, unless the radiators or pipes are corroding, in which case they will be producing rusty sludge and will need flushing more often. Having the correct levels of inhibitor in the central heating system should prevent rusting.

That being said, if you are using an inhibitor and still need to flush the system more often than once every 10 years, then it’s time for a complete new central heating system! Just getting a new boiler is not a good idea if the radiators and pipes are already badly corroded, bite the bullet, get a complete new system, and use a good rust inhibitor from day one!
Yes, the fuel burned by the boiler makes no difference, all types of central heating systems using wet radiators can be power flushed.
No, this is not recommended as it will actually add oxygen and other impurities to the water, which ultimately promotes corrosion and therefore sludge!
Yes, this is good practice after any disturbance of the boiler, radiators, valves or pipes. But the amount of air in the radiators afterwards is usually quite small. But bleed the radiators as normal never the less, to ensure optimum heating system performance after the power flushing.
It's mostly rust from corrosion in the metal pipes and radiators, but also contaminants from the water supply. So using a good inhibitor can actually help to prevent sludge build up.
Maybe! Boiler noises can be caused by scale or debris accumulating on the heat transfer surfaces, so in these circumstances if you can remove the debris or scale with power flushing, then you will remove the source of the problem. However, it may not be debris or scale build up that is causing the noise, it could be corrosion for example which will not be cured by flushing, or the noise could be down to any number of other problems.