Cold at the bottom, warm at the top? That is sludge.
If your radiators have cold patches, the boiler bangs or kettles, or the property takes an age to warm, the problem is usually not the boiler. It is black magnetite sludge sitting in the base of the radiators — and it is costing you money on every gas bill.
Indicative cost
Typically £450–£750 depending on the number of radiators.
Priced by radiator count rather than by the hour. A magnetic filter and corrosion inhibitor are included in every flush — without them the sludge simply returns and the expenditure is wasted.
What actually happens on the day.
A power flush is not a plumber turning a tap. It is a pump connected to your system, driving chemicals and high-velocity water through every radiator until what emerges runs clear.
Is a power flush even the right answer?
Sometimes it is not. A radiator cold at the top rather than the bottom contains air and requires bleeding — a five-minute task, not a £600 one. If the system is otherwise sound and a single valve has seized, that is a valve. We inspect before flushing, and if you do not need one, we will tell you.
Completed within a day.
No walls are opened. No radiators are removed. Heating is restored the same evening.
Diagnosis first
We take a thermal reading of every radiator. Cold at the base indicates sludge. Cold at the top indicates air. Only one of those requires a flush.
Fixed price
Quoted by radiator count, fully inclusive — chemicals, magnetic filter and inhibitor. No additions.
The flush
Pump connected, chemicals circulated, every radiator flushed individually until the water runs clear. Typically 4–6 hours.
Filter & protect
Magnetic filter fitted, inhibitor dosed, radiators re-balanced. We will show you the water that came out — it is genuinely striking.
The questions people don't ask out loud.
So we'll answer them here instead.
Is a power flush actually worthwhile?
If the radiators are cold at the base and the boiler is banging, yes — it is the difference between a system costing you money every month and one that does not. Absent those symptoms, probably not, and we will say so rather than take the work.
Will it damage our old pipework?
On a very old system with corroded pipes, an aggressive flush can occasionally find a weak joint that was going to fail regardless. We inspect first and, where the system appears fragile, recommend a gentler chemical flush instead. What we will not do is begin pumping without looking.
How will we know it worked?
You will feel it — radiators heat evenly and the property warms faster. You will also see it: we take a thermal reading of every radiator before and after, and you will see the water that emerged. That evidence is difficult to argue with.
“Three radiators had never heated properly in six years and we had assumed a new boiler was required. They showed us the water coming out of the system — it resembled used engine oil. The house has been noticeably warmer since, and the gas bill fell.”
Tom H. · Power flush, Wimbledon
Power Flush — straight answers.
Typically £450–£750, priced by radiator count. That includes the cleansing chemicals, a magnetic filter and corrosion inhibitor — anyone quoting substantially less is likely omitting one of those, which means the sludge returns.
Usually four to six hours for a standard property, so a single day. Heating will be restored that evening. Larger systems with many radiators can run longer.
The classic signs: radiators cold at the base but warm at the top, a boiler that bangs or kettles, radiators slow to warm, or dirty black water when bleeding them. Radiators cold at the *top* simply contain air and need bleeding rather than flushing.
It should. A system clogged with magnetite forces the boiler to work harder to move less heat. Clearing it delivers the same warmth for less gas. It will not transform your bills, but on a badly sludged system the difference is noticeable.
Only where a magnetic filter and corrosion inhibitor are installed afterwards — which is why both are included in every flush we carry out. Without them you are back where you started within a couple of years.
Radiators cold at the bottom?
We'll confirm whether you actually need a flush before selling you one. If it's simply air in the system, we'll tell you.