My parents have a 30 year old heating and DHW system consisting of a floor standing Potterton gas boiler (45kBTU) and Primatic Cylinder. The running costs of the system are proving significantly high. In conjunction with adding improved lagging to the primary and cylinder, I wondered whether it is possible to add a cylinder stat and zone valve to the return of the primary (along with improved programmer) allowing separate heating and DHW. I realise that Primatic's can be sensitive, but I can't see why this should affect the air-lock, but just wondered if anyone had any advice or experience. Thanks