Hello im just wondering if you can help im a bit stuck ive been out to a power flush and i had warned that it may not work so i went done the flush and still the same proplem which is "the system is a conventianl boiler, back boiler the customer rang me on sunday he fitted a new pump but the rads still didnt work,the hot water is off gravity so when i went i checked the water level in header tank all ok,i bled the rads all filled up ok then i turned downstairs off andput heat on the rads got hot but as soon as turned downstairs on only the kitchen rad got hot,i found that its pumping over when pump on 2 or 3 it just doesnt sem to be circulating now when i looked at the pipework at the back boiler on the flow is a old fitting which is about 3" long 22mm and has a vent in the middle which a vent key fits but do you think it could be some sort of dumblift valve. When the system nees venting the tank is reblenshing ok and i tried banking the expansion and cold feed just to see if it circulated when it couldnt push over but no joy,any ideas boys i spent all day flushing it and did get a hell of a lot of sludge out and the customers told me it is better but i cant get it to heat up when all rads are on,all rads will heat up if others turned off and ive balanced it right down