The short version
- Cold at the bottom of the radiator points to sludge; cold at the top points to air
- A magnetic filter after the flush is what stops the problem returning
- Price is driven by radiator count and system condition, not by the postcode
- Some systems only need a chemical clean, not a full power flush
The symptoms that justify a flush
Sludge is iron oxide from inside the steel radiators. It settles low and slowly blocks flow.
- Radiators cold across the bottom but warm at the top
- Some radiators never get hot while others are scalding
- Noisy pump or banging pipes when the heating fires
- Dirty black water when you bleed a radiator
- Repeated boiler lockouts on overheat or low flow
Power flush vs chemical flush
A chemical flush circulates cleaner through the system on the existing pump and then drains it — appropriate for a lightly contaminated system. A power flush uses a dedicated high-flow pump with flow reversal to physically shift debris out of each radiator, and it's the right choice when radiators are already blocking.
What drives the price
Radiator count first, system condition second. A ten-radiator house with severe sludge takes most of a day; a six-radiator system in fair condition is a half-day job. We take before-and-after temperature readings so you can see what changed.
Making it stick
A flush without a magnetic filter and inhibitor is a temporary result. The filter catches the iron oxide that will always be generated; the inhibitor slows the corrosion producing it. Both are also warranty conditions on most new installs.
Common questions
How long does a power flush take?+
Typically four to eight hours depending on radiator count and how bad the sludge is.
Will it fix a cold radiator for good?+
Combined with a magnetic filter and fresh inhibitor, yes, in most cases.
Do I need one before a new boiler?+
If the system water is dirty, yes — most manufacturers require a clean system for the warranty to stand.
Can it damage old pipework?+
We inspect first. On very old or fragile systems we'll recommend a gentler chemical clean instead.
Cold radiators? Get them looked at
We'll test flow and temperature before recommending anything.