Power Flush FAQs

A power flush is a deep clean for a central heating system. A machine pushes water and cleaning chemicals through the radiators and pipework at high flow to lift out sludge, the black magnetite that builds up as the system slowly corrodes, then the system is refilled with clean water and a corrosion inhibitor. There is a full explanation on our power flushing in London page.

Most domestic power flushes take roughly half a day to a full day. It depends on the number of radiators, how dirty the system is and how easy it is to reach everything. A heavily sludged system takes longer because each radiator needs more work to run clear.

There is no fixed schedule. A system that is kept protected with inhibitor and a magnetic filter can run for many years without another flush. The honest answer is to flush when the system needs it, not on a timer, which is why we test the water rather than assume.

Yes. Cleaning chemicals loosen the sludge and scale so the flow can carry them out, and a corrosion inhibitor goes in at the end to protect the system afterwards. The products are made for heating systems and matched to the job.

The usual signs are several radiators cold at the bottom, black water when you bleed them, or a system that is slow and sluggish all over. One cold radiator, or a radiator cold only at the top, usually means something smaller. Our symptom checker gives an honest first read in under a minute.

Not always. Radiators cold at the bottom point to sludge and often do. A radiator cold at the top is trapped air and just needs bleeding. We check which pattern you have before recommending anything.

Black water confirms corrosion, but the right fix depends on how far it has gone. Lightly tinted water may only need inhibitor or a filter, while thick black water with cold-bottom radiators usually does point to a flush.

Often not. A single cold radiator is more likely a stuck valve, trapped air or balancing than a whole-system problem, so a full flush would be the wrong fix. We diagnose before recommending system-wide work.

It depends on the number of radiators, the condition of the system and access, so there is no single figure. We confirm a clear quote for the agreed work before anything begins, and you can see what affects the figure on our power flush cost page.

Very low fixed prices often cover a quick chemical circulation rather than a thorough flush, or they leave out the extra time a heavily sludged system needs. We would rather quote honestly for the work your system actually needs than advertise a headline price that changes on the day.

We give a clear quote for the agreed work before we start. If a heavily contaminated system turns out to need extra cleaning or further work, we explain it and agree it with you first, rather than promising unlimited work for one price.

On a sound system, a properly carried out flush is gentle. On fragile, very old or microbore systems there can be a risk, which is why we assess the system first and use a gentler method where a full flush would not be wise. There is more on our can a power flush damage old pipes page.

Most can, but not all should be. Some older or weaker systems are better suited to a gentler chemical clean, and occasionally the honest advice is to plan a repair or upgrade instead. We tell you plainly what suits your system.

It can occasionally reveal a weakness that was already there, such as a pipe or joint already corroded thin, rather than create a fault from nothing. Assessing the system first is how we manage that risk and discuss it with you before any work begins.

Not if the system is protected. A corrosion inhibitor slows new corrosion and a magnetic filter captures any magnetite that still forms, so a cleaned and protected system stays clean for years.

It is the best way to keep a cleaned system clean, because it captures magnetite before it can settle again. On many systems a magnetic filter plus inhibitor is excellent ongoing protection.

Often the system should be cleaned before a new boiler goes on, so the new boiler is not connected to sludge and dirty water. A full flush is not always needed though, so it is worth checking first what the system really needs.