Honeywell motorised valve not working correctly?

[SJB060685]

It never stays in mid position after a call. If HW was last call then its returned to HW. If CH was last port of call its held in CH position. Theres a resistor and diode involved. I will upload an image, although its been shared before.

 

[John.g]

So it doesn't stay in mid position so as this is really not the "last port of call",

 

[SJB060685]

It holds the last point of call

 

[John.g]

I have no problem in understanding the last port of call if it has been in either CH only or HW only, on CH only the valve is (240V) kept energised by the grey wire via SW1 only (HW off) to keep it it in this position, on HW only the valve is in its unpowered state anyway so remains there.

If its in mid position, it is kept there by feeding 240V via the white wire through a diode and a resistor which reduces it to ~ 60/70 DC volts, SW1 is now also closed to the grey wire but no problem as no voltage from this wire. If you then switch off the CH first then the valve will return to its unpowered state which is HW, if you then switch off the HW there will be 240V on the grey wire but because SW1 is now opened from the grey wire then the valve will stay unpowered. But if you switch the HW off first then you will have 240V on the grey wire which will power the valve to CH only and it will remain there if you then switch off the CH, is this how it might work?.

 

[SJB060685]

Yes mate. That's not the best image but one I quickly found for you. Try these two.
If in mid position and you swith CH off. You will lose power to the white wire, which is what's holding the valve in mid position with pulses of DC. The valve will spring return to HW and close switch 1. If you turn off HW first then grey wire will supply 230 volts and fully motor over to CH position and switch switch 2 over supplying 230 volts to orange.
Whatever is the last port of call is held in either case. One of the problems with this design though is if CH was the last port of call the valve remains energised and motored over to CH, which is why they frequently burn out.

 

[John.g]

Thanks, that's what I thought might happen alright, so obviously cannot stay in mid position except calls for both HW&CH, still, a very ingenious design, it also has another resistor to give a AC de magnetizing current.

 

[SJB060685]

Thanks, that's what I thought might happen alright, so obviously cannot stay in mid position except calls for both HW&CH, still, a very ingenious design, it also has another resistor to give a AC de magnetizing current.

It does mate yes.

 

[spanner]

H/w is default position. If Last call was central heating valve stays until next call depending on cylinder stat satisfied and its hot water priority..