By all means point me at a good FAQ rather than answer the question!
The central heating pump is in the first floor airing cupboard. Pipework is generally 22mm.
Feed arrives and then enters a T with straight going into 15mm to the expansion pipe. Right goes about 4 inches to another T where straight is to the pump and the entering pipe is from the header tank (in 22mm). After the pump there is the motorised valve.
The expansion pipe goes up about 1.5m and then there is a "trombone" tube of about 1m before it drops back into the header tank. The header is probably only about 1.2m above top of hot water tank.
Of late it has started pumping over badly - the pump is set to the lowest speed.
Any suggestions why and, more importantly, how to cure it.
Thanks