If you have cold spots on one or more of your radiators, you may need to perform a power flush of the system. A power flush forces a high volume of water and cleaning product through the system to remove any debris that has formed there over time. This can be quite a complicated procedure that generally requires a professional, but do-it-yourselfers can go it alone. Simply rent a power flusher from a local tool shop, which can also sell you the cleaning product required.
Turn off the water and switch off the boiler. Locate the isolating valves that should be on either side of your central heating pump. Check your owner's manual if you are not sure what the central heating pump looks like.
Remove the pump from the boiler and using the instructions that came with it and connect the power flush system to the central heating system.
Turn off all of the radiator valves and open the air bleed valve to allow the air in and the water out. Lay old blankets and towels on the floor around the radiators to soak up any water that may leak out.
Connect the power flush to the valves on the tail of the radiators and you are now ready to power flush the system.
Set the dumping and overflow hoses over a suitable drain.
Add the cleaning product to the power flush unit, following instructions. Check that all radiator valves are open so that the water will be able to circulate.
Switch the power flush unit on.
Turn the boiler back on until the water has reached approximately 45 degrees then switch it off again. This activates the chemicals in the cleaning product.
Close off all radiators except one and allow the water to flush through. Repeat this process on all of your radiators.
Open all of the radiator valves and allow the water to flow freely until it runs clear.
Close all of the valves and disconnect the power flush unit. Reconnect all items that you removed from the central heating system.
Open all the valves and turn the water back on at the mains. Your central heating system is now ready to use again
Only attempt this project if you are confident that you can do it.