Radiator Sludge: How to flush a radiator and remove sludge

Summer has gone and Winter is here so it’s the ideal time to check your central heating and ensure your heating is as hot and as efficient as it can be so you’re ready for the cold weather. If you found that the radiators in your home were not as warm as they used to be but are still warm around the top and sides but cold in the middle and bottom then you probably have radiator sludge, something which will happen to most central heating systems sooner or later.

This will mean a colder home, higher energy bills, and the possibility of causing further damage to your central heating system.

What is radiator sludge?

Radiator Sludge DiagramRadiator sludge is a mix of dirt from water and iron oxide (rust) that results from the inside of your radiator corroding over time which settles at the bottom of the radiator and interferes with the correct flow of the hot water. You can see in the diagram to the right how the sludge restricts the flow and leaves some areas of the radiator cold.

Not only does this sludge create an inefficient heating system meaning you are spending more to keep your house warm but it can also damage the boiler, heat pump and valves which can prove very costly indeed. If your system is more than 10 years old then it’s highly likely you will have a build-up of corrosion.

How to remove central heating radiator sludge

There are two ways you can remove the sludge from your radiators:

1. Remove the offending radiator, take outside, and then manually flush it through with a hosepipe.
2. Professionally power flush the whole system.

Each method has pros and cons, and the option you choose will depend on your own DIY plumbing skills and also you budget.

Option 1: Manually flushing a single radiator

Pouring away radiator sludgeThis option is the cheapest and quickest to do if you feel confident removing a radiator yourself.  Before you remove the radiator ensure your heating has been off for a while as you don’t want to be dealing with scalding hot water.

When removing the radiator take care to protect the flooring and carpet as radiator sludge is very very dirty. Have a container ready to pour the radiator contents into and then you should take the radiator into the garden and use a hose to flush through the radiator and clean it out.

This method will remove the sludge from a single radiator but it could still mean that there is more sludge in the system so don’t view this as a long term solution. If you are getting sludge then it means you probably don’t have any inhibitor in your central heating system and this problem will happen again. Read how to manually flush your radiator here.

Option 2: Power flush the whole central heating system

Powerflush RadiatorThis second option will involve getting a plumbing and heating professional to power flush the system so is more expensive but is cleaner and will remove the sludge from all your radiators without having to remove them.

The engineer will attach the power flushing unit to the central heating system which produces a powerful, yet low pressure, flow which dislodges the sludge and sediment and removes it from your system. This will normally take around 4-5 hours but at the end of the flushing process the system will contain fresh clean water and be pH neutral. A corrosion inhibitor will then be added to the system and the engineer will balance all the radiators and check the system is working properly. A professional power flush will cost around £275-£350. Read more about power flushing.