Alpha CB28 Hot Water Problem

Hello, hoping for some expert advice about problem with my alpha CB28 (believed to be about 8yrs old, only been here for 18mths).

I have read, and read the posts with very useful info about what seems to be a fairly common problem with hot water failure but can only get so far working mine out ...

CH is working fine. When CH is on I might be able to get some HW but not very for any length of time and probably only by turning CH control right up to 9 max setting.

If I switch boiler to HW only, turn DHW tap on, then after initial cold water I get hot water briefly which then goes very cold.
I've unclipped the DHW flow switch (horseshoe clip) and if the DHW tap is on then the boiler fires up, the amber light is on constant but I only get vaguely tepid water. With the flow switch clipped in place the boiler doesn't fire up.
What do I need to do next to work out the problem or is this sufficient info to confirm what it is? This is the bit where I'm not sure about diverter valves, diaphragms, spindles etc.

Thank you in anticipation of some further help/guidance. Lisa

From what you have posted, the diaphragm is first and most likely culprit.

Ok, so I don't think I want to try and fix this myself.
How much should a job like this cost me to get a boiler engineer to fix and am i better off getting a specialist in to do the job or use someone like british gas for a fixed price?
I suppose I'm a bit worried I get his repair done and then the problem isn't fixed or recurrs or something else goes wrong...
I don't really want to spend any more than I have to to get me through the next 3 - 6mths as the plan has always been to relocate the boiler and replace it along with virtually everything else in the house!
Thanks again for any help/advice.

Since last night, I have now had a call to do one of these today!

If all goes well I expect it to cost around £90 + VAT.

Need to add, that I now don't get any hot water out of tap even with CH on. Does this make any difference along with the info given in my original posting or is fault diagnosis still the same? Thanks again.

Flow switch needs checking. Very common fault on these.

Prise it off the DV and if it is working the boiler will fire up immediately.

If it doesn't, replace the flow switch.

The flow switch is on top of the DV, a plastic horse shoe clip.

Thanks, but I already did this as per my original post. What I meant that was different now, is that the hot water doesn't really get hot at all now when the flow switch is operated, regardless of whether CH is on or not. Hope this makes sense. I wish it was just the flow switch as I could change that very easily myself, but I don't fancy tackling the diaphragm.