Mid position 3-port valve problem

[oilman]

Hello experts
I need some help

I have a diverter valve (4073A) which is doing something unexpected, (and I'm too lazy to look through all the previous posts).
If we start off with no power,
then turn on the power
and then select CH with the thermostat calling for heat,
the motor will open the valve and the lever will move across and start the pump and boiler.
If the DHW is selected,
and the cylinder stat calls for heat the valve will go to its mid position.
DHW stops calling, and the valve goes back to heating.

Now then, if the CH is turned off at the programmer or the room stat stops calling for heat, the valve stays at the heating position, though the pump and boiler stops.

The valve will return to its rest position only if the mains to the heating system is removed.

I have replaced the valve and the symptoms persist. There is probably a wiring fault, but I have not been able to work it out.

Any ideas?

 

[shaneo]

have u replaced the whole valve and not just the head?

if not was the valve able to move freely

 

[corgiman]

Oilman its my experiance that they always do this as the CH ON is not powered up but the HW off still is, so the grey wire has 240 which poweers the motor round the ch heating only.

If you were to turn HW on then the valve would go to HW only

No fault just design

 

[shaggy]

The valve is working correctly but it isn't the grey wire live causing the motor to power to ch. That only happens if the white wire is live as well when the room stat calls for heat. The last position of the valve was for ch which leaves dc current on the motor which stalls it. Switching on HW or turning off at mains will de-energise the valve and the spring pulls it back to HW only.

 

[shaneo]

who cares remember the 1st rule

if it aint broke dont fix it
it works, what more do u want

 

[MANDATE]

Hi oilman! I looked at this recently and agree that when CH is satisfied the valve remains at the CH positon until one of the other positons is selected, or the power removed altogether. There are two HW power feeds, when HW is on there are two options at the cylinder stat depending if HW satisfied. In addition there is the HW OFF which supplies power direct to the grey wire and it is this that holds the valve in the CH position. When CH is on it is being controlled by the room stat which cuts the supply to the orange wire when satisfied, but still leaves power to keep the valve in position in readiness for when the room stat demands heat again.
The reduced power using the diode/resistor works at the mid position, it's sufficient to stop the spring from returning the valve to HW only, but not enough to drive the motor forward to CH only.

 

[DP]

Oilman, that what the valve is supposed to do- stay in the last position when all demands are satisfied.

 

[oilman]

Thanks for all the info guys, seems I can't have seen how these were working.

Mandate, first paragraph describes what I had exactly, but the diode resistor is to provide d.c. to the motor which causes it to stop in the mid position. ChrisR found a description of this somewhere recently, but I can't remember where.

 

[shaggy]

I thought the dc current caused the motor to stall in the last position it was in, not to go mid-position?

 

[oilman]

Didn't say it went to mid position, I said it stopped there. The dc is switched in by something, and according to the info I've had up to now, the switch in question works at mid position. The CH is against the stop, and the other end of the travel is no power applied so it returns on the spring and stays there until power is on again.

 

[ChrisR]

CH4's contribution:
//www.diynot.com/forums/viewtopic.php?t=8369