Alpha CB28 Flow Switch or Diaphragm?

[pilotdavo]

I've had a good look through at the postings on the common problem of loss of hot water with the Alpha CB28 combi. Mine is 4 years old, no previous problems.

I have the same problem as many of the other postings. ie; CH works fine but DHW is intermittent. It started to do this just before Xmas.

From what I have read it seems to me that if the CH has to be turned on to get any DHW it is most likely the DIAPHRAGM that needs to be replaced.

And, if the DHW is intermittent and unaffected by the CH setting it is more likely to be the FLOW SWITCH.

Does this sound feasible? I'm going to open things up and have a feel of the outlets from the diverter valve to try to diagnose this problem further.

Any help greatly appreciated.

 

[ChrisR]

You should have found this one, same boiler and problem:

http://www.diynot.com/forums/viewtopic.php?t=42255

Dodgy flow switches, and small holes in diaphragms, can both give intermittent problems.
If you always get good HW by having the CH on then it isn't the diaphragm, (probably!).

 

[Agile]

I went to an Alpha recently and I thought that it was a CB model.

However, the one I saw had no diaphragm but instead a four pipe HE.

The DHW fault was caused by an intermittent DHW thermistor.

Only two months later we were called for another fault and found it to be the CH thermistor which is craftily hidden inside the combustion chamber to make it a job for a CORGI.

Tony

 

[ChrisR]

That would have been a c23/c27.
I did include "probably" - there to cover more obscure faults, and my ignorance...