Hi, new to the forum ( first post ) have tried to search but could not find the topic , so hear goes . I have a Keston C36 its about 7 years old and the hot water produced is not as good as it should be . I am wondering if the DWH plate heat X is not as good as it should be , the keston shows the primary flow temp and DWH temps on the control panel the difference betwwen the two is round about 18 deg c . The question (finally) is this ok or should i suspect silting up ? thanks in advance regards to all .... :