Thank you for your help.
I'm on a course for plumbing and the teaching is a bit, well, wet! I've got an exam tomorrow and this was part of my prep, but i've found the answers... would you have got it?
What is the likely problem arising from a bypass not being fitted to an open vented close-circuited fully pumped heating system controlled by 2 X two port valves on the heating and hot water circuits?
a) 'sucking down' and 'pumping over' the open vent pipe
b) Blockage occurring in the cold feed pipe
c) Rapid pinhole corrossion of the radiators
d) No cool water from the f&e cistern if the system overheats
Answer............
D