Hi there im a gas installer ,have a prob on a baxi 133 he plus ,when the hot water is ran after a while once the boiler is starting to get upto a hot temperature it starts making a screeching noise , figure it may be the diverter valve and them o rings again, or poss the pump not circulating enough ,this prob only occurs on hot water heating works fine , water gets hot just the noise starts ,any u guys out there ever come across this one before,dont really want to start changing part after part till i suss it any input will be much appreciated.