can anyone tell me with a heating tank if u put a blank on the expansion and lets say cut in a gate valve for the feed. is this sufficient to flush the system as its only at low pressure, iv never done one of theis before only a combi.
Yes just blank off the vent pipe. If you fit any kind of isolator to feed you shoudl really remove once you have finished so as cannot be accidentaly turned off. Although in practice most are left in place anyway.
I would use a FULL BORE ball-o-fix valve rather than gate valve. Something that cannot be closed off without taking tools with you otherwise the gate valve could just be turned off and the boiler circuit compromised. BOOM.