SMC twin pump (I think) Central Heating Prob

[Niggy]

Ollski, just re-read your post.....

I'm sure I havent seen an anti-gravity valve - would I be right in thinking that this would be located between c/h pump and where it goes up through garage ceiling to h/w tank?

If there is not an anti-grav valve + non-return valve is jammed open would this explain my symptoms??

 

[kevplumb]

yes you need to drain system if you can get the cover off and clean the valve should solve your problem
there should be two valves btw which may be the problem