desludge my central heating system?

This need not be too expensive, or difficult to do.
If you can drain your heating system, and refill it yourself, then you are capable of flushing it.
Firstly, drain the system. then add a bottle of FERNOX SLUDGE REMOVER AND CLEANER (two if you have a big system), refill the system, bleeding all the radiators.
Leave the chemical in the system for a week (have the heating on as normal as the chemical works better when it is hot), and then drain the system again. Refill the system, turn the heating on and when all the radiators are hot, drain it down again. This should remove all the chemical and any remaining debris in the system.
If your heating system is blocked or has poor circulation (maybe a couple of radiators not working), then a power flush might be required. This is when a machine is connected to your system with a big pump on it to force cleaning chemicals through the radiators and pipework. This is time comsuming and costly. However, despite what British Gas salesmen(sorry, engineers) say, most systems dont need this.

The boiler man
February 2009