pump washers are easy providing your pump valves either side are not seized. as for sludge you can d.i.y with fernox ect chemicals that you buy from your plumbing centre or have it powerflushed depending how bad the system is, how bad is the bottom of the f/e tank in the loft, or are you starting to burst rads.
powerflushing is about £350 upwards. we do standard house 8 rads for £350 providing all rads and valves are in good working condition.
hi-spec plumbing, October 2006