Central Heating Problems - Honeywell ST699 & V4073 Valve

Discussion in 'Plumbing and Central Heating' started by simacc, 26 Nov 2008.

  1. simacc

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    I am having problems with my central heating and having a go myself to fix it. The main parts are as per the subject a Honeywell ST699 timer and a V4073 Mid Position Valve.

    My partner and I have been living at the property for 11 months now and about a month ago we kept on getting caught out in the morning with no hot water. Everything was fine before and we could time the heating and the hot water separately.

    Now the water doesn't heat properly and the heating doest seem to respond to whats going on with the thermostat. We also noticed that the timer was not switching on and off and was sometimes not switching off when it should have. The hot water was also coming on when the heating was and vice versa (I think!). I got my multimeter out and checked that the correct voltages were being swtiched to the valve and it didnt looked like it was. From my memory the heating wire to the valve was going from 0-150V and the hot water was not doing anything.

    I thought this may be due to the timer not doing its job properly so got another one from ebay and fitted it thinking it would solve all the problems. Unfortunately it doesnt look like it has. I have just tested the heating with the thermostat turned right down and the radiators are red hot. I have also noticed that it sounds like the boiler and pump switch on as soon as I plug in the timer, is this right? One test I was going to do was to see if the valve was moving manually. With the old timer it looked like the mechanism on the valve was moving where as with the new one it doesnt.

    I hope I have provided enough information for someone to be able to help (and not bored you too much!!). I cant see that there is a wiring problem as it was working in the past, which is why I was pointed towards the timer. Now I have ruled it out (I think), I'm now thinking its the valve.

    Any help would be greatly appreciated.

    Si

    EDIT: I have just noticed the boiler and pump being active it due to the cylinder thermostat. If I turn it down then everything shuts down, as soon as you hear a click when turning it up (meaning its reached the current temp) then it all kicks off again. This is without the heating or hot water being switched on.
     
  2. gas4you

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    Sorry too long a post for my attention span :oops: but I would suggest it is the 3 port valve head that is faulty.
     
  3. Slugbabydotcom

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    When you swapped programmers did you swap like for like? ST699 for ST699?
    Did you replace the backplate and mix the wires up ?
    Only 150v suggests dodgy wiring, a bad connection or dodgy relay in your programmer.
     
  4. simacc

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    Thanks for your reply. Yes I have swapped like for like. I have noticed that the incoming live from the fused spur is only 150V, which is a bit strange. I was doing some more tests yesterday evening and the valve looks like its turning both ways and to the centre when both are switched on.

    I did, however, notice that when the valve was turning anti-clockwise the mechanism was rubbing against the lever that sets the valve to 'auto' or 'manual' and in most cases would rub so much it would knock the lever into 'manual' mode. I set both the heating and hot water to come on this morning and it all worked fine!

    This now begs the question, is the ST699 I bought off ebay faulty?!
     
  5. gas4you

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    Personally I think everyone who buy's off ebay needs their head testing :LOL:

    The grief caused just to save a few pounds never ceases to amaze me :eek:

    You need to check to see if you have 240VAC going into the fused spur first then logically trace this into the heating circuit.
     
  6. simacc

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    It was a bit more than a few quid, I got it for £23 so saved about £50!

    I'm going to borrow another multimeter to make sure its not the equipment measuring the voltage incorrectly too.
     
  7. gas4you

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    What people tend to ignore is the fact that, in your case, it was £23 for a reason, at best second hand or nicked, at worst faulty.
     
  8. simacc

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    true. looks like the later in my case.... :(
     
  9. D_Hailsham

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    That's one heck of a voltage drop!
    1. Unplug the ST699.
    2. Measure the voltage at the fused spur.
    3. Measure the voltage between terminals 1(Live) and 2(Neutral) of the backplate.
    4. If you are not getting 240v in both cases, check the tightness of all connections. If this does not give you 240v, you need to get your wiring checked from the fuse board/consumer unit.

    If you do get 240v, test the ST699
    1. Check that you have a wire connecting ST699 terminal 1 to terminals 5 and 8.
    2. Trace the wire from ST699 terminal 3 (CH ON) to a terminal in the wiring centre and disconnect all other wires on that terminal.
    3. Replace the ST699, turn power on and turn CH ON and continuous at the ST699.
    4. Measure voltage at the terminal in the wiring centre. It should be 240v. If it is, the CH ON terminal of the ST699 is basically OK, but check it with the CH on the various options (timed etc) to make sure it is not a timer fault.
    5. Reconnect the wires.
    6. Trace the wire from ST699 terminal 6 (HW ON) and disconnect any other wire. Measure voltage on that terminal with HW ON, as above. This will check the HW ON side of the ST699.
    7. Reconnect the wires
    8. Trace the wire from ST699 terminal 7 (HW OFF) and disconnect any wires found. Measure the voltage on the terminal when HW is turned OFF. Should be 240v. Check it gives the same result when turned off by timer or manually.
    9. Reconnect the wires.

    If everything checks out, your ST699 is OK and the fault lies somewhere else.
     
  10. simacc

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    Wow, thanks for the reply, really really useful. The main problem I was having was finding where the problem lies in the system, as Im not an expert I was having trouble fault finding. Now I can atleast find out whether the ST699 is faultly (both new and old).

    Love this forum!
    :D
     
  11. D_Hailsham

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    You will find Honeywell Wiring Guide very helpful as it has fault finding tips for the Y-plan, which you have.
     
  12. Slugbabydotcom

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    The diverter probably wont funtion with only 150V going through it. Are you running the system through an extension cable or something?
    Whatever , sort the voltage out before you go any further.
    Long cable runs and coiled wires cause resistance which reduces voltage.
     

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