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central heating won't turn off

Discussion in 'Plumbing and Central Heating' started by macwales, 17 Oct 2018.

  1. macwales

    macwales

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    I have a Gloworm Flexicom 18hx boiler, Drayton T721R Programmer, a Drayton MAI/679-3 3 PORT VALVE and a Drayton RTS2 thermostat and a Drayton cylinder stat.

    The programmer, 3port valve and both thermostats are all new.

    The hot water system is behaving correctly, switching off with the cylinder stat at correct temp and off when the programmer switches to hot water off mode.

    My problem is that the central heating switches on OK when the programmer goes to a CH on cycle but stays on when the programmer is in a central heating off mode. Something is firing up the boiler when there is no demand. The thermostat appears to work when CH on cycle is operating but has no effect when heating is on when there is no demand from the programmer. The 3 port valve stays in CH position when the programmer has no demand for CH.

    In this state, switching off the mains power to the programmer interupts the power that is holding the 3 port valve in the CH position and the 3 port valve springs return the valve to the hot water position. This turns the CH off and when power is restored to the programmer the central heating is off until both programmer and room stat call for heat.

    Then all works until end of next central heating cycle and then programmer should switch central heating off but it stays on continually, with radiators getting very hot.

    Help needed please.
     
  2. hertsboilers

    hertsboilers

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    If you turn on hot water only, and see the boiler is firing, the position of the valve should be at W. If not, the valve is faulty.
     
  3. D_Hailsham

    D_Hailsham

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    The valve staying in the CH position, after CH has been satisfied, is a feature of the 3-port mid-position valve. When CH only is ON, the voltage to the boiler is supplied by the valve's orange wire, fed from the white wire. When CH goes off, the voltage to the white wire is removed, but the orange wire still has a much reduced voltage on it. This voltage is normally not enough to switch the boiler on.

    The problem is either in the 3-port valve (too high a voltage on the 3-port), or on the boiler (fires up when voltage is below 240Vac).

    If you have a multimeter (and know how to use it), check the voltage on the orange wire when CH is On (240Vac) and Off (50-150Vac). If the Off voltage is higher than 150Vac the problem could be the valve. If below 150Vac, the boiler is probably the problem.

    It might be worthwhile contacting Glow-worm and checking if this is a known problem with the Flexicom boiler/ Drayton valve combination.
     
  4. stem

    stem

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    Then I suspect, that possibly they haven't been wired in correctly. Why were they changed? Was there a fault before, and if so what was it? You are quite right when you say:

    When unpowered, the motorised valve is held by a spring to close the central heating outlet.

    When central heating is required, the motorised valve receives power (on its white wire) from the room thermostat via the programmer to operate the motorised valve motor and open the heating outlet.

    If the thermostat, or programmer go 'off', the live should be lost and the spring pulls the valve back to close off the heating port.

    It's possible, if it's been wired in wrongly that there is still a live on the white wire when there shouldn't be. Someone with electrical knowledge and a multimeter would be able to physically check this.
     
  5. macwales

    macwales

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    Thanks for the replies. I will check the voltage on white and orange wires.

    3 port valve was changed because the plastic body and internal plastic parts of the permanently fixed actuator had disitegrated as it was 20 years old.

    New two part valve and actuator was carefully wired to same terminals in wiring centre as the old one.
    The old room stat was broken and new one fitted to existing back plate and is working
    Programmer was changed to check the fault was not programmer

    The cylinder stat was changed as old one was letting hot water get too hot and new one works

    In all cases wiring was to same terminals in wiring centre and checked against y plan diagrams and fitting instructions.
     
  6. macwales

    macwales

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    Thanks for the replies. I will check the voltage on white and orange wires.

    3 port valve was changed because the plastic body andvinternal parts of the permanently fixed actuator had disitegrated as it was 20 years old.

    New two part and actuator were wired to ssme terminals in wiring centre
     
  7. macwales

    macwales

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    Results of voltage tests

    White wire 3 port valve at H with no programmer demand 0 (zero) volts

    Orange wire 3 port valve at H with CH programmer demand 115v

    Orange wire 3 port valve stuck on H with no programmer demand 115v

    Orange wire with 3 port valve at mid position with demand from programmer for hot water and CH 250v

    White wire wth 3 port valve at mid position with demand from programmer for hot water and CH 250v

    Is it wiring or faulty actuator or something else?
     
  8. stem

    stem

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    What voltage is on the white wire, when the heating is still running when it shouldn't be? ie, when it
    Please set the hot water to be off too when you do this test, so that the valve doesn't get power fed back from the hot water controls.
     
  9. macwales

    macwales

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    Thanks for the reply

    I will test this tomorrow morning. I will need to set CH only to come on with the programme timer for a few minutes, then wait for the programmer to switch to no demand for CH. The fault will make the CH stay on and I will test the voltage on the white wire.
     
  10. stem

    stem

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    OK, thanks. You didn't answer my earlier question question about why the programmer, motorised valve and thermostats were changed? Was there a fault before that you were trying to fix and, if so what happened?
     
  11. macwales

    macwales

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    Hi

    Answer to question from Stem


    'What voltage is on the white wire, when the heating is still running when it shouldn't be? '



    White wire zero volts.

    Note

    The system was misbehaving tonight so I did the test. Seems to work OK while CH is on with hot water as long as cylinder stat is calling for heat. When hot water reaches set temp the room stat looses the ability to switch off the CH. This is with programmer still on for CH. Then the boiler is on all the time and this continues when programmer timer turns off CH mode.

    In this state and with hot water turned off at the programmer, there is zero volts on the white wire. This is the situation whether room stat is on or off.
     
  12. macwales

    macwales

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    As far as why controls were changed please see post 5 in thread above.

    The present fault has been present since new 3 port valve was fitted. Before this change, heating was switching on by itself in middle of night when programmer off and moving plastic parts of old actuator were completely broken and loose parts were jamming the internal mechanism. The thermostats were changed last year and worked. The new programmer was fitted after the new 3 port valve was fitted and present fault present but this made no difference.
     
  13. stem

    stem

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    OK thanks, need to try and get my head around the info for a bit.

    So, just to confirm, the following were all true at the time when you made the test:

    1. The programmer central heating was set 'off'
    2. The programmer hot water was set 'off'
    3. The central heating was still running
    4. The white wire was at 0v
     
  14. macwales

    macwales

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    Correct.
     
  15. stem

    stem

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    Can you clarify what you are referring to "two part valve" please?
     
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