check for cold radiators, then check for cold spots in rads.
Normal process for sludge, is to clog up the base of the rad, so you would expect the rad to be HOT at the top and COLD at the bottom. This would indicate sludge,
thanks oliver for taking time to reply
reason i was questioning for power flush was that bt engineers said power flush was neccessary as my boiler was firing up every few seconds and cutting out they said system was sludged up
but my radiators are running perfectly so i wondered if it was neccessary to spend £700 which they quoted me
once again thanks ernie watson