Thanks for the reponse - much appreciated. Have 2 more plumbers due today!
Would incorrectly placed / too small a pump overrun creae a similar problem? valves are 2 way and I dont think pipework for overrun will hold much water before reaching valves (which would be closed)
The problem only...
I moved into a 1980's house a few weeks ago. The house has a Ideal Heat 30 boiler in kitchen with cylinder in airing cupboard and tanks in loft.
Under boiler there are 3 motorized valves, 2 for heating and 1 for HW.
The 2 heating valves are wired together into stat (as there arent seperate zones...