alpha 240x expert required

28 May 2007
Reaction score
United Kingdom
Hi guys, can anyone help,
i have a alpha 240x, and the dhw was passing over to the heating, changed the domestic diaphram and the full kit on the c.h. side. now when you run the boiler on ch demand , the pump runs the diaphram lifts but the boiler doesent fire, if you lift the dhw micro sw. the boiler fires and the ch starts to flow, let the sw go and the pump continues but the boiler shuts down, however the ch diaphram stays on demand with the clock on or off, if you now open the dhw the boiler fires and the dhw is hot so the water is now diverting as to the demand.
i,mm thinking the differential pressure sensor but ??

greatfull for any sugestions
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What do you mean you replaced the full kit?

You should have replaced the whole diverter valve behind the diaphragm housing as well as the diaphragm.
Hi Dave
changed the domestic diaphram, and the primary diaphram which comes with daiphram, new spring o rings etc

For this fault you will need a new DV, or as some do on here, a recon kit for the DV.

Personally I only replace with a genuine new part.

The parts you have replaced are control parts to tell the boiler to fire and that the pump is working. They will not cure the fault of the rads getting warm when a hot tap is run.
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If pushing the primary M/S fires the boiler the primary Diaphram can't be working correctly regardless of if it has been replaced or not
the primary diaphram lifts and falls with demand, but the boiler doesent fire, when you also lift the dhw diaphram micro sw. then the boiler fires

Maybe a daft question, but did you refit the microswitches in the correct places and not get them crossed??

Also, changing the DV solves the 1st problem.
micro switches are the right way, yes first problem ok, that,s why i thought the differential pressure sensor, have you experienced this ?
Worth a try, the way you describe the symptoms, it really does sound like you have attached the primary microswitch to the to the DHW housing and vice-versa.

I just cant see how changing a couple of diaphragms gives this problem.
You confirm that when you open a hw tap the pin comes out and operates the switch, followed by pump kicking in, then observe the primary pin operating the primary switch. The boiler should then go to fan, aps and ignition.
Turn on ch, the pump should start, the primary microswitch should operate then ignition sequence.

Primary FS = 2 red wires
DHW FS = 3 wire

Maybe you have a faulty DHW FS?
your a star, it was only when you said that i realized, i must have looked at the drawning 20 times, when you said that ! irealized i was checking the micro sw. and not the wiring, boiler perfect, just goes to show how easy it is to make a mistake.
Thanks again for your help & thoughts, you,ve made my day :D :D :D

Thanks also to everyone else for their help and idea,s
best regards,
hope i can help anyone else i future.

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