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Siemens 3 way valve

Discussion in 'Plumbing and Central Heating' started by RobDG, 18 Dec 2009.

  1. RobDG

    RobDG

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    Hi,

    Please could someone help. I'm having problems with central heating / hot water system in that the hot water just gets hotter and hotter when either hot water or central heating is on.

    I suspect the thermostat on the cyclinder... but took apart a 3 way valve to see if that was working. Can anyone tell me how these things work - what the manual and auto settings do and what I should expect to see?

    I have a Siemens 3pmp-v22 motorised 3 way valve.

    Many thanks!

    Rob
     
  2. Hugh Jaleak

    Hugh Jaleak

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    Manual setting is for holding the valve open when filling or draining the system. In normal operation it should be left at auto. Valve position in auto is at rest open to hot water, it'll move when the central heating calls for heat. If both are calling then it should be at mid position, open to both ports, when the HW is satisfied, (seems it might be!) then the flow should be diverted to the heating side. Once heating is up to temp then the system should shut down, until either CH or HW stat calls for heat again.
     
  3. RobDG

    RobDG

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    Many thanks. There are 2 microswitches, one nearest the valve and another next to it. Which controls the hot water and which controls the C/h please? When the switches are open (i.e. not pressed in), are the corresponding valves open also (I think I understood you said they were open)?

    Should the switch furthest from the valve ever oscillate open and closed? It seems to when both c/h and hot water are wanting heat....

    Very odd!

    Many sincere thanks for your help
     
  4. Hugh Jaleak

    Hugh Jaleak

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    I wont to confess to understand the intricate operation of motorised valves, D Hailsham is the man for that IIRC. I believe however the valve should operate the appropriate microswitch as it reaches the required extent of its travel, this in turn supplies the signal (power) to the boiler and pump telling it to fire/run.
     
  5. RobDG

    RobDG

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    Thanks - no problem. I think further diagnosis has uncovered the problem. The boiler and pump will ONLY fire up when C/H and Hot water are both on, cyclinder thermostat is on, and room stat is on. Then and only then does the 3 way valve close the switch closest to the valve - and the outer one oscillates on and off. A local electrician put in a new thermostat a while ago and its not been right since then. It did work perfectly before then and he says he had to do some "rewiring" of the system - and I suspect (to put it politely) that he b*ggered it up!

    Its 27 years old and the rads are old, so I think I'm gonna have to get the whole lot replaced :( ah well. Thanks for your assistance anyway! Very helpful

    Cheers
    Rob
     
  6. Hugh Jaleak

    Hugh Jaleak

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    If you are competant with electricity then there are a few checks you can do with a multimeter, there was a post on here recently with a good fault finding guide, just cant remember who wrote it!

    The wiring on these is rather complicated, it has to be done by the letter else (as you've found....) it dont work! For some reason its not registering the HW as satisfied, and the valve is not closing the HW port.....
     
  7. matt1e

    matt1e

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    Hi rob that makes two of us I reckon you have a problem with the stat and/or wiring too

    A quick description of how it works

    hotwater only
    A call for heat from the programmer will provide power to the boiler via the cylinder stat when the HW is up to temp then the stat will toggle over to satisfied and remove power to boiler, when it cools down it will toggle back and refire the boiler as necessary

    the valve plays no part electrically when on HW only

    hotwater and central heating
    now the valve comes into play,the boiler will be operated via the cyl stat as above but now the CH call will open the valve by providing power to the valves white cable
    where the valve opens to depends on what state the cylinder stat is in,but for now we will persume that the cylinder stat is still calling.
    so the cylinder stat is still calling and there is power on the valve white,so the valve opens, when it reaches half way (mid pos) it toggles over the first micro switch which switches in a resister/diode arrangement which modifies the ac waveform supplying the motor and stalls it
    so now we have the valve open mid position and the boiler is still being controlled via the cyl stat
    now two things can happen
    1)If the room stat becomes satisfied then power is removed from the white and the valve returns to the Hot water position again,blocking off the heating port
    2) if the cyl stat becomes satisfied then it will toggle over to the satisfied terminal which is also connected to the valve grey this restores the voltage to the motor and drives it to the heating position and blocks off the hotwater port
    this is where the second microswitch comes in,remember that the boiler was being supplied via the cyl stat,this power is removed when the stat toggles over,so now the boiler is fed from the roomstat via the second microswitch which is connected to the valve orange
    if the room stat becomes satisfied it now just removes power to the boiler as apposed to blocking off the heating port because the power on the grey holds it in this position
    if the cylinder stat calls for heat then power is removed from the grey,the valve winds back till it hits the first microswitch which then stalls it again at mid point if there is still power on the white(due to the modifyed dc waveform)
    on selecting CH only the valve is fooled in to thinking that hotwater is always satisfied by providing power on the grey when hot water is switched off and operates as described above
    so basically (omiting earth and neutral)
    white=drive to mid
    grey= drive to heating only(will only work if power is on white and at mid but will also hold valve at heating once there regardless of power on white)
    orange=connects to white when valve in heating pos and used to operate boiler(heating position only)
    hope I have explained it ok
    Matt
     
  8. matt1e

    matt1e

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    hi rob I forgot about your problem and it will be with the stat or stat wiring
    do you have a multimeter and are ok using it?
    matt
     
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    DIYnot Local

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