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Quick guide: what's a central heating powerflush?

A powerflush can improve the efficiency and lifespan of a boiler and central heating system, but what's involved? We asked recommend heating engineer Chris Ball.

Thermostat being adjusted

A quick guide to central heating powerflushing

What is a powerflush?

How much does a powerflush cost?

We surveyed central heating engineers in July 2012 and found that the average price range for a powerflush was £330-£450.

See our cost and completion time guide

A powerflush is a process carried out by central heating engineers which removes sludgy build-up in the parts and pipes comprising a central heating system.

This helps to improve the efficiency and lifespan of the boiler and central heating system and prevent breakdowns.

How do I know if my central heating needs a powerflush?

One or more of these symptoms could indicate that your central heating system would benefit from a powerflush: 

  • cold radiators with only a hot strip at the top
  • black sludgy water in the heating system (shown by radiator removal or a failed heating pump or valve replacement)
  • poor circulation to a system that used to work better
  • an overflowing attic header tank.

If you're having a new boiler installed but have an old central heating system with old-style radiators, then a powerflush could be a good idea.

Your boiler engineer can carry out visual and chemical checks which determine the PH balance and levels of corrosive elements in the system. These will determine whether a full power flush is needed.

Sometimes a 'dynamic flush', using clean mains pressure water, is all that is needed. 

What happens during a powerflush and how long does it take?

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A powerful machine called a pumping station is used to remove dirty water and sludgy build-up while introducing clean water.

The engineer may add a chemical to the system to break down sludge before the equipment is connected and the flushing process begins.

The powerflushing process is lengthy – you should expect the engineer to spend around 90 minutes flushing the whole system (in two directions) and then to tackle troublesome sections until they run clean.

After clearing out the system, a chemical neutraliser is added and, once washed through the system, the PH balance is checked.

Finally, a dose of 'inhibitor' fluid is added to the system. This prevents corrosion and goes some way in preventing the build-up of sludge in the central heating system.

Who should perform a powerflush?

A Gas Safe Registered central heating engineer should carry out powerflushing. You could have it done as part of the annual servicing of your boiler and central heating system or at any time during the year.

Look for recommended central heating engineers in your area and always get at least three quotes, remembering that the cheapest may not be the best.

About our expert trader

Chris Ball is a central heating engineer at Christopher Richard Ltd.

The business, based in Chertsey, Surrey, is an endorsed Which? Trusted trader having been given the stamp of approval by the scheme.

Which? Trusted Traders is an endorsement scheme that puts traders through a rigorous assessment and health check to ensure that the traders we recommend are trustworthy.