I have wall mountd worcster 30cdi - 3 yrs old .CH is working fine. the hot water supply pipe runs between dwn stairs ceiling & upstairs floor. It supplies -in order -ensuite basin tap ,power shower,bath tap ,basin tap then goes dwn stairs to cloakroom basin,utility sink tap then kitchen tap. If I turn on any hot tap *except bath tap * I get hot water , if i turn on another tap (except bath ) i continue to get hot water . however if I turn on the bath tap first I only get warm water ( a few second of hot at first ) if I turn on another tap the water remains warm from both taps , if I turn off the bath tap I will get hot water out of the other tap i opened . This has been happening for abt six weeks .I have had DHW sensor changed but no change . The only thing I can think of that may have happened to boiler abt six weeks ago ( but not sure exactly when ) the pressure was toppd up to 1.5bar instead of manuft recom 1.0bar . I droppd the pressure to 1 bar abt two weeks ago with no difference _so not sure if this even connected . Eng talking abt changing dhw exchanger plate ! (big job & expensive ! ) Anyone got any other suggestions plse .

Fred, January 2011

a simple way to check the boiler it to use a thermometer to take the temperature of the cold water and then the hot water and compare the results with the boiler specifications normally a boiler will raise the water temperature 35 deg C at its maximum flow rate as you can see this means that if the cold water temperature to your house is 4 deg. (which it has been since before Christmas ) then the hot water will be 39 deg. if the heat exchanger was faulty the burner would modulate up and down so as to prevent the boiler over heating

brian, January 2011

RE brians answer -the flow rate -11ltrs a min is spot on & hasnt changed .

fred, January 2011

and it's about six weeks ago that the ground water temperature dropped through the floor meaning the boiler has to heat the water more to reach it's designed temperature a combi is a one tap boiler however in the warmer months it can depending on flow rate serve two taps to illustrate my point simply turn on a cold tap and after a a couple of minutes feel the temperature the boiler has to heat this to approx.60.C in a few seconds check the recommended flow rate for the boiler (usually about 10 ltrs per min ) open a tap to this flow rate, use a measuring jug, and see if it gets hot if it does the boilers ok.

brian, January 2011