Hi, A new customer has contacted me stating a plumber fitted a new radiator for them recently and a few isolation valves and now their heating isn't working. I went out to view and couldn't see anything obvious other than the pump not circulating past its top valve. The only other thing is the old guy put an iso valve on the cold feed coming off the f and e tank, to Isolate it easier. There's a separate vent on it so as I understand there's no risk of pressure build up (correct me if I'm wrong) but has anyone heard of this causing issues with the heating? (air expansion etc.) Never come across it before and I would fit valves on the Inlet side of the tank so haven't had to deal with issues on the cold feed side. I told them I'd get back to them ASAP, but as far as I can see, the pumps had it. Any advice?