Trying to fault find Honeywell Y-Plan system

Discussion in 'Plumbing and Central Heating' started by The Jeep, 19 Sep 2006.

  1. The Jeep

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    Hi-
    I am trying to get to the bottom of a problem with a central heating Y-plan system. Basically, when CH and HW are both on at the programmer, the ch temperature rises uncontrollably, with the room stat displaying eratic behaviour.
    I have checked the voltages being output from the various components and have observed 186V on the orange wire from the mid-position V4073 valve, which is also present at the cylinder stat (terminal 1, I think).
    I will be going back to make a more thorough check today, but am I right in believing that the grey wire outputs 230V and the orange wire outputs around 100V when both CH and HW are on at the programmer but not calling for heat, in order to hold the valve in its last position?
    This voltage of 100V on the orange wire is also going to be present on the switched live to the pump and boiler, but I am assuming (?!) that this voltage is too low to operate either. However 186V, being significantly higher, is enough to operate both, hence the uncontrolled temperature rise. If this is the case, then it seems that I need to replace the V4073 power head.
    Basically, I would like some explanation of why 100V is designed to be present on the orange wire when 230/240V is on the grey alone, why this voltage does not affect boiler and pump on/off, and what the effect of a faulty 'too high' voltage of 186V might be. Many thanks!
     
  2. ChrisR

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    There's a diode and resistors in the valve head, so you do get "funny" backfed voltages.
    As far as the boiler is concerned, 0V is off and 230V is on, and it's only the orange wire which matters.
    The only valid inputs are
    0/230 on White (High = heating ON)
    0/230 on Grey (Low = hot water ON)

    See Y Plan

    Take the head off (assuming it has a pimple, see
    HERE )and see if the shaft is free to turn its 40 degrees or so.
    If the valve doesn't go where it should, which may depend on where it came from, microswitche(s) inside may be duff. Very hard to change so get a new head.
     
  3. justqualified

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    Voltages should be-

    Hot Water only - white-0v, grey,0v orange 230v

    Heating only- white-230v, grey- 230v, orange-230v

    HW and Heating- white-230v, grey-50/110v, orange 230v
     
  4. The Jeep

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    Thanks - I went back and took fresh measurements today and will submit a more detailed post later. In the meantime, however, the Honeywell V4073 technical blurb does state that:

    240V in grey wire = valve hold in last position + approx 100V on orange wire.

    It seems to me that any voltage present on the orange wire will be felt by the pump and boiler. So how do they respond to this voltage?

    I should add that, on rechecking, the 186V was not on the orange wire (which I have only ever measured 0 or 240V on - never 100V), but on terminal 2 of the cylinder stat during 'temp fall' when C and 1 are made. As this terminal is connected to the grey from the mid-position valve, this may well be a back-feed voltage and nothing to worry about (?).

    As I said, I will submit more details later, but in the meantime would be interested in an explanation concerning the above point about the 100V (I have emailed Honeywell about this but have not yet had a reply).

    Thanks again for all assistance offered!
     
  5. simond

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    You dont say what the boiler is.

    Some units (such as the old Worcester 28 CDi system boiler) have electronic sensing on the PCB - rather than a relay - which is sensitive enough to trigger on the orange of a Honeywell 3 port from the low voltage 'leak'.

    In the case of the Worcester they used to suggest you go to your local capacitor retailer and buy a 4.7 micro farad to ground the signal.... how convenient.

    This is not the case on their newer range. The German boilers (and 28CDi was a German one) tend to be sensitive to this as they were not designed to work with Honeywell, many system boilers use the internal 'combi' diverter valve for the heating/hw selection in a system boiler and have a three pipe connection in Germany.
     
  6. bster

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    This may or may not be of some help

    Honeywell state that:-

    "Low A.C voltage may appear on specified wires or terminals due to backfeed from V4073A valve. If in doubt disconnect grey and white wire as appropriate, or check with meter for full 240v".
     
  7. ChrisR

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    Somewhere I have the internal circuit for a 4073, wil look.
    If the boiler and pump were wired old-style, in parallel, the low pump resistance would probably knobble any high-resistance supply on the orange wire, so the boiler would see very little.

    the voltage "back fed" to the cylinder stat would just end up at the output relay/terminals in the programmer . I don't think they're ever a problem.

    But then I didn't realise some boilers would react to 100V - must have always used 2 ports with those!
     
  8. andsam

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    Had something similar. Honeywell diverter sending approx 130v to Baxi Solo PF 3 that sometimes fired the pump and boiler.

    Solution 1

    The seimens 3 port diverter valve dosent send this stray voltage down the orange wire.

    Solution 2

    You can fit a capacitor between the Switch live and neutral at the boiler which will stop any low voltages triggering the boiler.
     
  9. ChrisR

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    Great! You couldn't use any old capacitor, it would have to be designed for exposure to full mains in the event of a short in the valve. Not many are, especially at 4.7uF.

    I would have thought that a boiler "noise suppressor" would do a pretty good job, could be designed for going across the mains, and of course is relatively easier for us to get hold of. I'll see what I can find. The only one I can think of offhand is for an Ideal Sprint.
     
  10. The Jeep

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    Guys, I'm going to try something here...I'll just explain, very briefly, the problem and see if it rings any immediate/obvious bells with anyone. More detail can be gone into later, like boiler type, etc (it's an old boiler, no PCB as far as I know: won't be able to check till Thursday):

    HW only on, the system works fine.

    CH only on, the system works fine.

    HW and CH both on, after a short while the following happens:

    - when cylinder stat is satisfied, the CH room stat works fine, whether calling for heat or satisfied (i.e. turning the temperature dial produces predictable results such as turning the dial down the orange 'on' light goes off).

    - when cylinder stat is calling for heat, if the room stat dial is turned DOWN, the orange light stays on (i.e. it's still calling) and when the dial is turned back up, the 'click' point has increased (i.e. it is sensing the temperature as having increased by more than it should - difficult point to explain I'm afraid!). Basically, the room stat is unable to be satisfied, hence the CH keeps rising uncontrollably, until the cylinder stat is turned down or is satisfied (still clarifying this last point - will check further Thursday).

    The problem my client has reported is that the house gets very hot when both HW and CH are programmed to be on at the same time, so he just programs them to come on separately, which is not ideal.

    Any bells ringing yet with anyone? I look forward to any constructive suggestions, or indeed questions...ta.
     
  11. Paul Barker

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    This is going to be a very shallow response, but I can only think that the problem lies in the electronics of the mid position valve.

    After you have proved to yourself that the cyl stat provides mains at the call for heat and the no call for heat at the appropriate time and the roomstat provides mains at the call for heat at the appropriate time, the most likely event is that the electronics inside the midposition valve are doing something strange. A simple thing to try is to take along a new whole valve, wire it in dry and observe it's behaviour and the systems behaviour, put the system through it's paces and see if that fixes it. If you are right, change the head.
     
  12. chrishutt

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    These might be helpful. I have versions showing live connections for each of the many states, which I can post if helpful.
    [​IMG]
    [​IMG]
     
  13. The Jeep

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    Thanks guys, those last two replies are particularly useful.

    Fistly, Paul, I agree: it is most likely something wrong with the electonics in the power head of the mid position valve, thus sending out strange anomolous voltages. I will try wiring in another one as you suggest.

    Secondly, thanks Chrisbutt for that very informative diagram: the first I have seen with detail of the valve head circuitry. Please do send me the info on expected voltages present at different states of system operation. I think that would help me understand what's happening better (all good stuff this!).

    I feel sure the problem will be cracked soon and my client will be delighted, especially as the problem has existed for some years, and I'm doing it largely as a favour. I'll be having another look at it tomorrow and will report my findings then, so please don't go away! Cheers, Jeep.
     
  14. chrishutt

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    That's what the lower diagram in my previous post shows. The various live connections are as follows -

    http://i89.photobucket.com/albums/k238/chris-clifton/yplan_next.gif
    http://i89.photobucket.com/albums/k238/chris-clifton/yplan_ch1.gif
    http://i89.photobucket.com/albums/k238/chris-clifton/yplan_ch2.gif
    http://i89.photobucket.com/albums/k238/chris-clifton/yplan_dhw.gif
    http://i89.photobucket.com/albums/k238/chris-clifton/yplan_dhw_ch1.gif
    http://i89.photobucket.com/albums/k238/chris-clifton/yplan_dhw_ch2.gif
    http://i89.photobucket.com/albums/k238/chris-clifton/yplan_end.gif
    http://i89.photobucket.com/albums/k238/chris-clifton/yplan_off.gif

    Not sure if they're in the right order in terms of operating sequence. You can work out what state each refers to from tail end of URL.

    The point about the operation of the mid-position 3 port is that the DC voltage coming via the diode locks the motor and thus holds the valve in the mid position, as in -

    [​IMG]
     
  15. The Jeep

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    Thanks very much Chrisbutt, I will study these thoroughly - excellent stuff! :D
     

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