3 way valve issues

[sotal]

Our 3 way valve has been causing all sorts of issues for a while now.

It was a Danfoss HSA3. The spindle had seized and was leaking.

So I removed it and replaced the body with a Honeywell V4073A that I had spare.

The V4073A was spare because I had purchased a complete body and head to replace just the head at our previous house.

So this has cured the leak but I currently have to turn the spindle by hand!

The easy answer to this would be to buy a replacement V4073A head to go on and wire it in place of the Danfoss head.

However I have the old V4073A head and a spare brand new synchro motor.

Am I a little too optimistic that just replacing the motor will sort it?

Currently if I wire the old head up in place of the Danfoss one then nothing happens when you switch on the heating or HW. The pump doesn't kick in or anything. I kind of expected it to work on one (is it HW that is in the default position?) Could it be the circuit board that has gone? Or is there anything else? If I move the manual slider across then the pump kicks in etc.

I take it the wiring matches between the two systems?

They were nearly the same, the V4073A had the addition of an earth wire, but otherwise the other 4 wires were very similar. I replaced Orange with Orange, Blue with Blue, Grey with Grey and white striped with white.

 

[sotal]

OK - Easy test done. I replaced the synchron motor with the new replacement and it made no difference.

I had a look at the circuit board but it is literally just 4 resistors and two microswitches. The resistors aren't likely to have blown and all look visually good. There are no dry solder joints. So that only leaves the switches - would these stop it from even starting? I would have thought they would be there to switch the pump on etc?

The only other thing could be the way I've wired it up. Does it sound right?

Thanks

 

[sotal]

Done a little more testing - when using the Honeywell head if I manually move the slider across it does kick in the pump but it goes straight back off as it bounces back - even if I put it on the little catch. In fact even if I hold it against the end. The initial momentum activates the pump but then it starts to wind back and goes off.

Any ideas what this points to?