Hi, I have a baxi 105e which has the usual problem with pressure rising and dumping through the prv. I have renewed the prv and thought my next step was to check diaphragm in expansion chamber but it appears there isn't one. so besides filling loop passing on valves could it be a problem with the other diaphragm on the hot water by pass valve, or is this not related to this type of problem . It currently needs topping up every day. Thanks for any replies