Central Heating Puzzle

Discussion in 'Electricians' Talk' started by David Morris, Aug 24, 2006.

  1. David Morris

    David Morris New Member

    My central heating system blew a fuse this morning.

    After I had replaced it, I found that the boiler worked fine and it heats the hot water tank perfectly. However, when the room thermostat calls for heat, nothing happens.

    I've checked the room thermostat and it is fine, the switch to turn on the room central heating also works fine.

    Any ideas as to why the heating doesn't come on?

    David
     
  2. Ripped Off

    Ripped Off New Member

    Pump or divertor valve not working as a starter for one
     
  3. David Morris

    David Morris New Member

    Thanks "ripped off"!

    The pump works fine when the water needs to be heated.

    When the rooms need to be heated, there is no sign of life in the pump.

    If it was the diverter valve, the pump would still be pumping wouldn't it?

    David
     
  4. DOES THE BOILER HAVE A SEPERATE PROGRAMMER?
     
  5. Ripped Off

    Ripped Off New Member

    What boiler have you got. If its a combi some dont have pumps on the hot water relying on mains pressure larger units have 2 pumps.
    Is there a cct diagram on the back plate or cover?
     
  6. fast

    fast New Member

    Ok, let me have a go.

    the pump is knackerd. your H/W is hot because of the gravity of hot water. H/W rises and cold falls keeping the cerculation going on the H/W side.
    But not the rads as they will not flow without the pump running

    HOWS THAT?????
     
  7. David Morris

    David Morris New Member

    Yes, there is a programmer in the airing cupboard separate from the boiler. I tested the switching function on that. It is OK.

    The boiler is not a combi. It's a 20 year old Glow-Worm. There's only one pump.

    Unfortunately there is no cct diagram. The wiring looks a bit of a cowboy job. A yellow/green wire is used as wiring to the switch in the programer! (but it's been that way for 20 years presumably)
     
  8. David Morris

    David Morris New Member

    I don't think it is the pump.

    I can hear the pump pumping when the water is being heated. When the radiators need to be heated, there is no sound from the pump.
     
  9. steve CF

    steve CF New Member

    Do you know what type of system it is i.e. "Y plan" , "S plan
     
  10. sinewave

    sinewave Screwfix Select

    Diverter Valve! ;)
     
  11. fast

    fast New Member

    David,
    Dose the orange conductor on the valve come live when you move the manual override arm on the side of the valve?
     
  12. Eye Squared R

    Eye Squared R Active Member

    David,

    It all begins with the 'Controller' switching a 'Live' to the Room Stat (Central Heating (CH)) and/or the Tank Stat (Domestic Hot Water (DHW)). If the Stat is closed (indicating a DEMAND) then this 'Live' is passed to the ZONE VALVE(S) which provides the supply to the motor winding and drives the valve open and at the end of its travel it closes a microswitch that then passes the 'Live' to the Pump and Boiler.

    If the CH isn't working then there is a problem with this sequence - the likely contenders are: burnt out Zone Valve motor coil and possibly the Zone Valve microswitch. You should be able to hear the action of the zone valve(s) when you switch the CH/DHW 'On'. A cheapo neon screwdriver is a very useful tool for chasing the lives around the system and a Wiring Management System allows you to fault find from the airing cupboard.
     
  13. Eye Squared R

    Eye Squared R Active Member

    David,
    Dose the orange conductor on the valve come live when
    you move the manual override arm on the side of the
    valve?

    Rewireking,

    the microswitch is not activated by the manual overide lever however there should be a permanent Live on the orange wire (common).
     
  14. britishblue

    britishblue New Member

    Eye, you said "the microswitch is not activated by the manual overide lever". This is not correct. When you move the manual override you can hear the synchronous motor being forced round and the switches clicking as they operate.

    BB
     
  15. David Morris

    David Morris New Member

    Rewireking: The orange wire does not become live when I manually move the lever across. It only becomes live when the hot water thermostat calls for heat.
     
  16. David Morris

    David Morris New Member

    Steve: Sorry, I've no idea if my system is "S" plan or "Y" plan.
     
  17. Ripped Off

    Ripped Off New Member

    What about G plan
     
  18. David Morris

    David Morris New Member

    Eye Squared R: That's very helpful thanks. I Haven't located the problem yet, but you've told me how to look for it.

    David
     
  19. sinewave

    sinewave Screwfix Select

  20. David Morris

    David Morris New Member

    Rewireking: correction, if I move the lever absolutely as far as it will go and wiggle it, then the orange wire does become live. I guess that indicates a fault in the diverter valve?
     

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