It’s important to keep your radiators working properly, so they can keep you warm through the winter. If you’re having problems with your heating, your radiators might need a power flush.

There are several symptoms that show you might need a power flush. If your radiators are cold at the bottom and hot at the top, you could have sludge blocking your radiators or pipes.

Sludge might also be to blame if some radiators aren’t warming up while others work properly.

You’ll find information below about the causes of sludge in your central heating system. We’ll also explain the power flushing process.

Diagram of a radiator showing 1. sludge accumulated at the bottom, 2. a cold area above it caused by sludge, and 3. other areas that warm up as usual

Why is there sludge in the radiator?

The older your central heating system is, the more likely it is you have sludge in your radiators.

Blocked radiators make your bills higher, as your heating has to work harder to warm your home. Sludge can also damage your boiler, heat pump and valves.

  1. Radiator sludge is a mix of dirt and rust. This builds up over time and gathers at the bottom of your radiators.

  2. The sludge stops hot water flowing through your system properly. This creates cold areas on your radiator.

  3. Other areas of the radiator are unaffected by the sludge and warm up as normal.

How does power flushing work?

If you think you have sludge blocking your radiators, get a Gas Safe registered engineer to have a look.

If you need a power flush, the engineer will connect a machine to your system. This will push a powerful, low pressure flow of liquid through your system. This dislodges sludge and rust, removing it from your radiators and boiler.

It can take several hours to flush out your radiator system. It can take even longer if you have a larger system or there’s a lot of sludge.

Your central heating system will contain fresh, clean water after the power flush. The engineer will probably add an inhibitor solution. This liquid chemical will stop sludge building up again.

If you’re experiencing other problems with your heating, our guides show you how to bleed a radiator and deal with other common radiator problems.

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Our one-off service has a fixed price that includes the call-out fee and labour. All our engineers are Gas Safe registered and you can choose an appointment to suit you.