DHW problem BAXI 105 instant

[Rankers]

Been having issues with the DHW from my Baxi 105 instant. Basically if I run the hot tap from a mixer tap (kitchen(cant tell brand - generic mixer), bathroom(damixa) or shower(mira combiflow)) the tap will run warm turning cold, guessing this is preheat reserve or warm pipes. If I run the bath tap, (single hot/cold) it will 8 times out of ten turn hot, then I can run the shower and sustain the heat turning the bath off. The only other way I can get the boiler to recognise hot demand is to run a tap, then turn the preheat to 0 then back on again; or turn the boiler on/off/remote/taps switch to a different setting.
Had a service to no real joy. help?!?

 

[baxpoti]

Hot water diaphragm needs replacing.

Lots of similar posts on here

 

[Rankers]

apologies but the exact model of boiler is a 105HE, would you be able to advise where I could obtain the diaphragm from or a part number?

Many thanks for the earlier reply,..

 

[baxpoti]

Baxi Prt No. 248838 Try online.

or complete unit 248734 (much easier and quicker)