Biasi M90e24S hot water problem

[Scrum-Master]

Hi,
I have a old Biasi M90e24s boiler that doesn't fire up when hot water is demanded. It works fine on Central heating. I have read the previous threads on here and gone through the issues.
When the hot water tap is turned on the fan and pump runs the red light on the flow switch is on the diverter valve makes a noise the primary circuit flow switch pin does come out but not far enough. Pressing the micro switch manually and it does fire up.
Since that the diverter valve has been overhauled so have a new diaphragm installed. Also at the same time the heat exchanger has been descale. Dont know how effectively inside but the holes are shiny now. It worked fine for approx a day then started showing the same symptom when hot water tap is turned on. The pin doesn't come out enough to make contact with the micro switch for the boiler ignition. With a plier can pull the pin out fully and doesn't feel like anything is stuck behind it that's preventing it from coming fully out.

Any suggestion? Thanks

 

[Deleted member 267285]

Was lubrication used on the pin when overhauled? If it’s not coming out far enough to make the microswitch there’ll be a reason why.

 

[Scrum-Master]

Silcone grease was used on it but not the pin itself. I am able to pull on the pin with a plier and it does come out. Could there be any other reason why its not coming out fully?

 

[Agile]

The usual reason is that the diaphragm chamber behind the pin is blocked up with dirt. When opening the diaphragm might already be damaged or may become damaged. The pin should move freely within it's gland.

There was another fault that the little hollow screw on the left has become loose and needs to be gently screwed back in.

Although rare the pump might not be running at full torque. Sometimes the start/run 2.6 uF capacitor looses some of its capacitance.
As originally supplied the pumps do not have any switch on them. After many years it is possible the pump has been replaced with a non original one which has a speed switch. If so this should always be set on the fast position III