Heating only on with water

Discussion in 'Plumbers' Talk' started by Ed Knox, Feb 13, 2021.

  1. Ed Knox

    Ed Knox New Member

    Hi,

    I just moved into a new house with an F&E setup. The central heating pump only comes on when the hot water is on and the cylinder thermostat is set higher than current temp. As soon as the cylinder reaches temp or the hot water is turned off the pump shuts down and stops circulating water to the rads.

    I've replaced the room thermostat. And I've prelaced the power head on the 3-port valve. The spindle turns fine, so I am assumed the mechanical but if the valve is ok.

    Any ideas from there? Is it maybe the wiring now either from the boiler or from the control unit?

    Any help much appreciated. In already cranking the hot water up to 80 just to keep the heating on! I'll need to run all the hot taps to drain the cylinder next!
     
  2. Teki

    Teki Screwfix Select

    Do you have access to a multimeter and how competent are you at working with electrics?
     
  3. kiaora

    kiaora Screwfix Select

    Hi
    It may be a 3 wire diverter valve, they have hot water priority,
    Or a 5 wire mid position that’s got a fault on the wiring

    good luck
    Peter
     
  4. Ed Knox

    Ed Knox New Member

    I have a multi-meter and can use it fairly well.
     
  5. Ed Knox

    Ed Knox New Member


    It was a 5 wire powehead that I replaced. So I guess it's a wiring issue? As we only just moved in I can't say for certain that it ever worked correctly.
     
    kiaora likes this.
  6. Teki

    Teki Screwfix Select

    Have you been able to identify where each cable goes in the wiring centre? Can you post a clear photo of inside it?
     
  7. kiaora

    kiaora Screwfix Select

    Hi
    With hot water only, looking only at the 5 wires from the valve, only the orange should be live, 240ac to neutral, if any other one are live you have a fault
     
  8. terrymac

    terrymac Screwfix Select

    If you set programmer for central heating only , does boiler not fire up / radiators not get hot ?
    Did you replace a complete actuator head ,or just the motor ?
     
  9. Ed Knox

    Ed Knox New Member


    struggling to upload a photo...Not sure the photo will be clear enough anyway. If it helps it looks like the orange from the valve is connected to a blue/yellow from the cylinder thermostat (and a red from the boiler I think but hard to trace). The grey from the valve to a blue on the cylinder thermostat. The white connects to a yellow that I think is coming from either the control unit or room thermostat. Blue connects to a blue and earth to earth. Not sure that helps! I'll test the orange with the hot water off as suggested. But should it be connected to the cylinder thermostat if it is the only one meant to be live?
     
  10. Ed Knox

    Ed Knox New Member

    Hi,

    With central heating only radiators don't get hot. Boiler seems to fire (less intently) but not the pump so no flow. I only changed the motor. The spindle was turning freely so assumed the valve was ok.
     
  11. terrymac

    terrymac Screwfix Select

    Your 3 port valve isn't functioning ,it may be knackered or it is a wiring / control issue. As you don't know the history ,you will need to do some testing at the wiring centre . What wiring centre do you have , is it a Honeywell ?
    Post pics of wiring at wiring centre ,in sharp focus so we can see the terminals and wires connected to them all.
     
  12. terrymac

    terrymac Screwfix Select

    Just noticed your earlier post with wiring info.
    With programmer set for central heating only ,and the room stat calling for heat ,the white wire should have 230volts ( measuring to neutral) . That powers the motor in the actuator ,which opens the valve to the heating port. Within the valve a micro switch is then made ,which allows 230 v down the orange wire ,which is in the terminal block that contains a wire that goes to the boiler ,and takes the voltage to the boiler for it to fire up. The boiler would usually ( internally) fire up the pump.
     
  13. BillyBobToo

    BillyBobToo Active Member

    You also require a hot water OFF to move the valve to heating only position.
     
    terrymac likes this.
  14. Ed Knox

    Ed Knox New Member

    Thanks, it's helpful to have something to test! So, hot water off, heating on and room stat calling for heat I have 230-240V on the white wire. But only 63V on the orange?

    When I switched the hot water off I paid a bit more attention. The boiler shut down straight away even though the room thermostat was calling for heat. The pump kept running maybe a minute before shutting down too.

    Also, having looked at images of a wiring centre online I realise there are proper units to help hold the wiring in properly. Mine is just a length of junction boxes. But I guess in theory should be able to do the job.

    So, with only 60odd volts going through the orange is that likely to indicate my issue. Is it that the valve isn't opening to make the microswitch? Or is the other thing wired to the orange (a blue and yellow from the cylinder thermostat?) Stopping it firing up the boiler maybe?
     
  15. Ed Knox

    Ed Knox New Member

    I read this article

    https://www.freeheatingadvice.com/a...al operation, with a,split or divert the flow.

    Which was helpful. The grey wire seems to be fine (energising when both heating and hot water on but when the hot water reaches temp and stops calling for heat). They bit works fine (I can hear the valve motor when the cylinde thermostat changes to call heat. The boiler fires for either hot water and heating or just heating when the cylinder stat is turned down).

    Do you think there is any point changing the cylinder thermostat? It is an old one. It seems more likely to be an issue with the valve but as I already swapped in a brand new actuator that seems odd.
     
  16. Mike83

    Mike83 Screwfix Select

    The grey wire should have 2 wires connected with it.
    You say the grey wire has a blue in with it from the cylinder stat.
    It should also have a wire it in from terminal 1 on the programmer.
     
  17. Ed Knox

    Ed Knox New Member

    Ah. So the grey only has a blue from the cylinder stat connected to it. Looking at a wiring diagram for my controller (Drayton SM2) terminal 1 is 'HW OFF'.

    So that should connect to the grey from the valve and blue from the Honeywell cylinder stat? I'll have to try and trace it as the wires coming up through the floor are spaghetti (boiler is on first floor)
     
  18. Ed Knox

    Ed Knox New Member

    Any ideas how I can double check I have the right wire if I think I've found it? Should it be live when the Hot water is on or off?
     
  19. Mike83

    Mike83 Screwfix Select

    I would visually check if there’s a wire connected at the programmer in terminal 1 and note the colour.
    Then try identify it.
    Terminal 1 will be live when the hot water is switched off. When the hot water is switched on there will be no power at terminal 1 as it switches down terminal 3.
     
  20. terrymac

    terrymac Screwfix Select

    The boiler fires for either hot water and heating or just heating when the cylinder stat is turned down).[/QUOTE]
    This is quoted from one of your earlier posts. Please explain ??
     
    Last edited: Feb 14, 2021

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