three port valve weirdness

[mikethepipe]

bit embarassed to ask-but here goes-what is going on with a three port Danfoss which doesn't return to hw only when "asked"? Replaced actuator,as I had done about 15 months ago,and all working.Checked hw off wire goes to grey actuator wire and all ok.
The grey wire ( I believe ) stalls the motor when live,so when hw on at programmer,this voltage on the grey wire is not present,allowing the return spring to take the valve motor to the rest position-ie hw.
The fault was showing up as a call for hw only sending heated water round the radiator circuit.
Also this problem only occurred after a ch only demand-mid way operation was normal
The wiring looked to be correct,and as I say a new head sorted it,but I,m concerned about the short life of the valve,and what failed and why,presumably the diode is ok as the mid position operation was normal,maybe a programmer fault-hw off voltage not turning off when hw on called for at programmer?
Sorry for long post-I suspect I am missing something blindingly obvious

 

[D_Hailsham]

How a three port valve works does what it says on the tin

You say that you have aconnection between the grey wire and the HW off but it must also be connected to the third terminal of the cylinder stat.

L641a, terminal 2 connects to wiring strip no 7 in this wiring diagram

 

[mikethepipe]

Thanks D.
So it looks like a failure to return to hw only when selected on the programmer - last post position being ch only-would indicate a voltage still being present on the hw off terminal,and therefore the grey wire would still be live.So maybe a faulty programmer contact? Thanks for your time

 

[MANDATE]

If you find a voltage on the 'grey' that you think should not be there and don't understand, it will be due to 'back feed', but has no effect on the operation of the valve. It's all to do with micro switches (MS)

The 'white' provides the power through 1st MS to drive the motor to mid point. It also provides the modified voltage through the 2nd MS to hold the motor against the return spring at mid point, when the 1st MS is triggered.
That is providing the 'grey' is not live. In this situation however the 1st MS drops the feed from 'white' and connects to 'grey'. The 'grey' is not connected at the cylinder stat or the HW OFF, but is connected at the 1st MS and therefore gets a back fed voltage from the circuit producing the modifed voltage, which comes from the 'white' wire via the 2nd MS.

 

[mikethepipe]

Ok.Thanks Mandate. All the information I need. Cheers

 

[mikethepipe]

Sorry Mandate-dont know if you will see this-been trying to get a wiring diagram worked out for the circuit inside the actuator-danfoss dont seem to have one-from your description the microswitches must be interlinked-2 way switching style? Also is there yet another m/switch to switch the orange wire?Sorry to be thick-but its driving me nuts-if i can just understand the circuit operation I'll have the beating of it in the future

 

[D_Hailsham]

Here are the Data Sheet and Instructions for the Danfoss Randall valves.

They cover a wide range of valves, so you need to identify your exact model.

 

[mikethepipe]

Thanks D for all your help.Have downloaded links.Cheers

 

[MANDATE]

Hi mike! There's just the two micro switches. They are set only a couple of degrees apart at mid position. So MS1 is triggered first and it then depends on the 'grey' being live or not. If live MS2 is triggered.
Both are like two way switches with a 'common' terminal and two other terminals. say L1 and L2.
MS1
The 'white' feeds L1 on MS1, The 'grey' feeds L2 on MS1. The output from 'common' on MS1 goes to the motor.
MS2.
The 'white' also feeds the 'common' on MS2. Output from L1 on MS2 is to the PCB to produce the modified voltage and from the PCB it joins the 'common' of MS1 (which is where the back feed occurs, cause it's connected to 'grey')
When MS2 is triggered ( cause 'grey' is live), output is now from L2 which is the 'orange', the PCB having no further role.
When CH only is selected and it becomes satisfied, the room stat cuts the supply to the 'white' so 'orange' has no output and boiler stops, but 'grey' is still live and valve stays put until room stat feeds the 'white' again.
Does all that make sense?

 

[mikethepipe]

He's got it by jove I do believe I've got it! Spent this evening doodling the circuit-it really is a simple circuit once you've worked out the sequence-I now finally know how the motor is held stationary-my brother in law is a very experienced plumber,and of course he knew chapter and verse about what colour wire goes where etc-but he couldn't explain the actual operating process,I was trained,many years ago as a mech.eng.technician,and it unfortunately left me with a slightly obsessive need to know WHY something had failed!Mandate-you're a gent-well beyond the call of duty-much appreciated.Mike