Alpha CB28 DHW micro switch/diaphragm problem?

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3 Apr 2011
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Location
Birmingham
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United Kingdom
I have an alpha CB28 boiler. The hot water only works when the CH is on too, and then not always.

From what I have read on here my understanding is that I probably have a problem with the DHW flow micro switch, or the diaphragm inside the diverter valve assembly.

Can someone tell me about the DHW flow microswitch. I have unclipped it, and tried pressing it, with and without a hot water tap on. The switch looks fine, and clicks, when I press it, but it does not ignite the boiler or seem to do anything. (whether the hot water tap is on or not). Does this mean the switch is broken, or could it still be the diaphragm?
Thanks in advance for any help.
 
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does the pin where the mico switch is move in and out with the hot water being turned on
 
there is no pin.

if the switch doesn't turn the boiler on when it's removed then it or the pcb is fecked. switch is cheap, pcb isn't. link the switch out with a bit of wire to prove it.
 
does the pin where the mico switch is move in and out with the hot water being turned on

When the micro switch is unclipped, no pin is visible in the hole. I am looking in form front, but can't see from above.

With the boiler switched to HW only mode, I have tried switching it on and off at the mains, with the micro switch unclipped.

When the mains is switched on, without me touching the unclipped micro switch, it keeps going through ignition cycles for a few seconds, then stopping.

However, if it's switched on while the unclipped microswitch is presssed, it stays silent, and doesn't do anything.
 
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sounds like microswitch is ok

but as this not being activated by hot water being turned on indicates possible DHW diapragm perished or sticking divertor valve.
 

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