the expansion pipe in my feed and expansion tank is overflowing when my pump is at 2 but not when its at 1. the problem is when the pumps at 1 the downstairs radiators do not warm enough. they do at 2 but back to the problem, the hot water then comes out of the expansion pipe. this only happens with the hot water and not the central heating. the three port valve seems to be working fine and the expansion pipe and the cold feed is in the correct place. help!
There could be a build up of sludge on the walls of your pipes. Or sometimes there is a gate valve on the return from the cylinder which could be restricting the flow too much. Have you got an auto by-pass fitted. Also you can change your central heating pump to one which slows down when pressure in the system starts to increase.