In resiting my boiler I'm putting in some improvements. One is to introduce some way of isolating the radiators from the boiler so that if I have to drain the boiler I don't have to drain the whole system. My plan is to put valves in the Flow and Return close to the boiler. However, I bought some 22mm Isolation Valves but noticed that the actual bore is nearer 15mm and I'm worried they would restrict the flow too much. My alternative would be to use Gate Valves, but would these be any bigger bore. Any advice appreciated.