heating
Power flushing and system cleaning
A power flush costs £350 to £700 for a typical house, priced by the number of radiators. It is worth doing when radiators are cold at the bottom or the water runs black, and it is a waste of money on a clean system where a chemical flush and a filter would do.
What this covers
Typical price. £350 to £700 depending on radiator count
What the job covers
- Full power flush of a heating system
- Chemical flush before a boiler change
- Magnetic filter supply and fitting
- Inhibitor dosing and water testing
- Diagnosing cold spots and circulation faults
What is involved
Sludge in a heating system is magnetite, an iron oxide produced as steel radiators corrode from the inside. It settles at the bottom of radiators where the flow is slowest, blocks the narrow waterways of a modern heat exchanger, and jams pumps and valves. It is the reason a boiler that was fine last winter locks out this one.
A power flush connects a pump and a magnetic filter across the system and drives water through it at high velocity, reversing the flow and working one radiator at a time to lift the deposits and carry them out. A chemical flush is different and much cheaper: a cleaner is dosed into the system, circulated for an hour or a few days, and drained. On a lightly fouled system that is enough; on a badly sludged one it dislodges material without having the velocity to remove it, and the boiler filter then does the work.
What prevents a repeat is not the flush but what happens afterwards. A magnetic filter fitted on the return catches magnetite before it reaches the boiler and gets emptied at each annual service. An inhibitor dose stops the corrosion producing the sludge in the first place, and it depletes over time, which is why it should be tested and topped up whenever the system is drained. A system flushed and then left undosed is back where it started in three years.
Full power flush of a heating system, one of the jobs a power flushing specialist is hired for.
Choosing someone for the job
Ask what the price includes: number of radiators, magnetic filter, inhibitor and a water test afterwards. Ask whether a chemical flush would do instead, and be suspicious of anybody who says every system needs a power flush. Ask for a before and after water sample, which takes a minute and is the only visible evidence the work did anything.
Common questions
Do I need a power flush with a new boiler?
Most manufacturers require the system to be cleaned to a standard, and a chemical flush plus a magnetic filter usually satisfies that on a system in good condition. A power flush is for systems with visible sludge symptoms.
How long does a power flush take?
Four to eight hours for a typical house, longer where radiators are heavily fouled and have to be worked individually.