How much is a power flush, and do you actually need one?

A power flush is priced on the size of the system rather than as a flat fee, which is why quotes vary so widely. This page explains what drives the number, and how to tell whether you actually need one.

What drives the price

The number of radiators. This is the single biggest factor. Every radiator has to be isolated, flushed individually and then brought back into the system. A two bedroom flat with five radiators and a four bedroom semi with twelve are very different days' work.

The state of the system. A system flushed as preventative maintenance takes a fraction of the time of one that has been running twenty years with no inhibitor and radiators half full of magnetite. Badly sludged systems sometimes need radiators removing and flushing outside.

System type. Open vented systems with a feed and expansion tank in the loft take longer than sealed systems.

Access. Radiators behind fitted furniture, or a boiler in a loft, add time.

What is included afterwards. A flush that finishes with a fresh dose of corrosion inhibitor and a magnetic filter fitted is a different job to one that stops when the water runs clear. The filter is what keeps the system clean afterwards.

Anyone quoting a power flush without asking how many radiators you have is guessing.

Do you actually need one

Not every system does, and a flush is sometimes sold when a chemical clean would do. The genuine signs:

• Radiators cold at the bottom, warm at the top. That is sludge lying in the base. Cold at the top is air, which just needs bleeding.

• Some radiators never getting hot while others are fine

• The boiler kettling or rumbling

• The system taking a long time to warm through

• Black water when you bleed a radiator

• The boiler cutting out on overheat because water cannot circulate

The black water is the clearest single indicator. That is magnetite, iron oxide produced as steel radiators corrode internally, and it is abrasive as well as obstructive.

Power flush, chemical flush and mains cold flush

These are not the same thing and the difference matters when comparing quotes.

A chemical clean circulates a cleaner through the system for a period, sometimes days, then drains it. It is cheaper and can be enough on a lightly contaminated system.

A power flush uses a pump connected to the system to push water and chemicals through at high flow rate, reversing direction to shift debris, working radiator by radiator. It is the thorough option.

A mains cold flush is what a lot of "flushes" included in cheap boiler installations actually are, and on a dirty system it achieves very little.

Why it matters before a new boiler

Modern condensing boilers have narrow waterways in the heat exchanger. They are far less tolerant of debris than a cast iron boiler from thirty years ago.

Fit a new boiler onto a contaminated system and the sludge migrates into it. A blocked heat exchanger is expensive, and every manufacturer treats it as a system fault rather than a boiler fault, so it is not covered by the warranty. This is why we treat the flush and the filter as part of a boiler installation rather than an upsell.

What good practice looks like

• The system is tested before and after so there is evidence it worked

• Radiators are flushed individually rather than the whole system in one pass

• The flow is reversed to shift debris that sits against the direction of normal flow

• Corrosion inhibitor is added at the end, at the correct dose for the system volume

• A magnetic filter is fitted, and then cleaned at each annual service

Without that last step the system starts filling up again from day one.

Getting a price for your system

We price on radiator count and system condition after looking at it, and we will tell you honestly if a chemical clean would do instead.

See our central heating repairs and radiator repairs and installation pages for related work. We cover Manchester, Salford, Stockport and the surrounding towns.

Ring 0161 515 9977 with the number of radiators and we can tell you roughly what is involved.