Power flush: what is it, why do I need it & how much is it?

A power flush is a way of cleaning and maintaining a central heating system by flushing chemicals through the boiler, radiators and pipework. Its purpose is to remove sludge and other foreign debris which may have built up inside the system, reducing its efficiency and potentially causing damage

Power flush overview

Over time, oxygen in the water of the central heating system will react with the metals internally to produce rust and other oxides. The end result of this chemical reaction is a black, muddy substance called sludge.

Sludge in a central heating system can produce all kinds of problems. These range from radiators which don’t get hot, to irreversible damage to the boiler. Limescale is another unwelcome compound which can form inside the system and cause similar problems.

This is where a power flush comes in. Power flushing involves pumping chemicals through the heating system at high pressure – higher than the system normally operates. This dislodges and dissolves the sludge.

How do I know if I need a power flush?

Power flushing should be carried out every 5-6 years. Signs that you may need it include:

  • Radiators which don’t get hot at the bottom
  • Grey, discoloured water when you bleed the radiators
  • Cloudy tap water
  • Your boiler is making unusual sounds
  • The central heating system takes a long time to heat up.

How long does it take?

A good power flush will take around 4-5 hours to carry out. However, it may take longer if there is a lot of sludge or your central heating system is large. At any rate, you should expect it to take up the bulk of the day.

The engineer may pump several chemicals through the system. These may include a chemical to dissolve the sludge and a descaler to remove any limescale. Once the power flush is complete, a good engineer will add an inhibitor to the system. As the name suggests, this is a chemical which inhibits the reaction between oxygen and metals. By doing so, it prevents sludge from forming in future.

If the sludge is particularly bad, the movement of the chemicals through the system may not be enough to shift it. This will require the affected radiators to be disconnected, removed from the wall and cleaned out manually with a hose in the garden.

How much does a power flush cost?

Generally speaking, you should expect to pay £300 – £500 for a power flush. This will usually include the cost of the labour, plus the cost of the power flush chemicals, which may be £50 – £80. However, extra work on parts of the system which are discovered to be badly clogged after the quoted price was agreed may invoke additional labour costs. For an extra fee, the engineer may also add a MagnaClean filter to the central heating system. This is a device which uses a magnet to collect iron compounds. Once collected inside the device, they can then be easily discarded.