Advice
Power flush: needed, or upsold?
A genuinely useful job with a slightly grubby sales reputation. Here's how to tell which one you're being offered.
What it actually is
Over years, the water in your radiators reacts with the steel and produces a black iron-oxide sludge, the consistency of wet soot. It settles in radiator bottoms, clogs pipework, and grinds away at the boiler's pump and heat exchanger. A power flush pumps cleaning chemicals through the system at high velocity to shift it, radiator by radiator, then refills the system with fresh water and inhibitor.
The three real signs you need one
- Radiators cold at the bottom, hot at the top. The sludge is literally lying there. Bleeding does nothing, because air rises and sludge sinks
- Black water when you bleed. Crack a bleed valve with a tissue underneath. Clear or pale yellow: healthy. Black or dark brown: that's your system's blood test coming back bad
- Kettling. A boiler that rumbles and bangs like an old kettle is boiling water around sludge and scale deposits. It's inefficient and it shortens the boiler's life
Got one or more? A flush will make a difference you can feel, usually within a day: faster warm-up, even heat, quieter boiler.
The signs you're being upsold
None of the above, but the quote includes a flush anyway "as standard" or "while we're at it"? Ask what symptom it's treating. An evenly heating system with clear water doesn't need one, and "the system's ten years old" isn't a symptom, it's a birthday. The honest exception: before a new boiler install, a flush (or at minimum a thorough chemical clean) genuinely is standard practice, because feeding old sludge into a new heat exchanger is how warranties get voided.
Cost, and what must be included
The price scales with your radiator count, so ring with the number of radiators and you'll get a quote on the spot. Whatever the figure, two non-negotiables in any quote: inhibitor chemicals added after the flush, and ideally a magnetic filter fitted on the return pipe. Skip those and the sludge starts quietly rebuilding the day the engineer leaves, and you'll be buying the same flush again in five years.
Not sure which camp you're in? Describe your symptoms on the phone and we'll tell you straight, including "you don't need one". Ask the central heating page's favourite question: what symptom is this treating?