Intermittent Hot Water Alpha CB28

[Gruffalodad]

I have a problem with my Alpha CB28. 5 Years old. Last year DHW started to get intermittent. With CH on, open hot tap – the water would run hot then go cold. Sometimes the water would not run hot at all. Changed the DWH sensor (fig 25, page 25 in manual) all fine till this year and it appears the problem has returned.

What do the experts think, time for another sensor, (are they that short lived!) or flow switch (fig 23) or maybe DHW flow valve diaphragm (fig 27).
Opening several hot taps and using the reset sometimes works.

 

[Rob]

All 3 parts could be tested so no need for guessing!

 

[gas4you]

I'd replace the diaphragm

 

[Gruffalodad]

How do I go about testing 3 three parts to isolate the root cause Rob?

The instruction manual is not that helpful to pinpoint the exact cause. I have read through the history of similar probs but none seem to be the same as mine. e.g. the intermittent hot water is independant of CH being selected.

It also seems to be sensitive to the temperature selected, turning the DHW selector to max and selecting reset can obtain hot water.

What is the real pain is that it will go for days behaving perfectly, then reappear, then work fine again.