Power Flush Cost: What Decides the Price

First, do you actually need one?

Before worrying about cost, make sure a power flush is the right job. The classic signs of sludge are radiators cold along the bottom, black water when you bleed them and a boiler that rumbles or kettles. But a cold radiator can also be caused by air, a stuck valve or poor balancing, which are much smaller fixes.

Our guide to a radiator cold at the bottom and our boiler kettling guide help you work out whether sludge is the likely cause.

Number of radiators

A power flush cleans radiators one at a time, then the whole circuit. Each radiator adds time, so the size of the system is the most obvious factor in the price. A two-bedroom flat with a handful of radiators is a much shorter job than a large house with radiators in every room plus towel rails.

How bad the sludge is

A system with light discolouration may clear quickly. One that has been neglected for years, with radiators heavy with sludge, needs more cleaning chemical, more time on each radiator and sometimes individual radiators removed and flushed separately. You do not always know how bad it is until the flush starts, so ask how a quote handles a system that turns out worse than expected.

Type of system

Sealed systems, which have a pressure gauge on the boiler, and open-vented systems, which have a small feed and expansion tank in the loft, are flushed slightly differently. Open-vented systems can need the tank cleaned or checked as well, since debris often collects there.

Microbore pipework, the thin pipes found in some homes from the 1970s and 80s, can block easily and may take more care to clear.

Condition of the pipes and radiators

A power flush runs water through the system at a higher flow than normal. On old systems, that can reveal weak points such as a corroded radiator or a tired valve that was only holding because sludge was sealing it. A careful engineer checks the system first and will tell you if parts are likely to need replacing. Sometimes a gentler chemical cleanse is the better choice.

What should be included

A fair power flush quote normally covers:

• Connecting the flushing machine and the cleaning chemicals
• Flushing each radiator in turn until the water runs clear
• Draining and disposing of the dirty water properly
• Refilling, venting and checking the system for leaks
• Adding inhibitor to protect the system afterwards
• Rebalancing radiators so they heat evenly

Extras worth considering

Fitting a magnetic filter at the same time adds to the cost but protects the money spent on the flush, because it catches any new sludge before it settles. Replacing sticking radiator valves while the system is drained also saves draining it again later.

Cheaper alternatives

For lightly contaminated systems, a chemical cleanse circulated by the system's own pump, followed by draining and refilling, can do the job for less. Taking off and flushing a single problem radiator is cheaper still if only one or two are affected. A good engineer will suggest the least work that will actually solve the problem.

Before a new boiler

If you are getting a new boiler, cleaning the system is usually expected as part of the installation, and many manufacturers require it for the warranty. In that case the flush is often quoted as part of the boiler job rather than separately. Our boiler installation page explains more.

Need it sorted? Book a power flush

We do not publish fixed prices because systems differ so much. Tell Chris how many radiators you have and what you have noticed, and he will explain whether a power flush is the right option. See our power flushing page, call or WhatsApp 07429 632804, or use the quote form.