Replacing dial thermostat? My dial thermostat has black, red & earth wires, what should go where in a replacement programmable thermostat?


Sorry to those who answered, but I have now taken a photo of the dial thermostat.

As can be seen, the red goes to the terminal right of centre while the black goes to the left of centre. The assumed earth has green and yellow sheathing and obviously is connected to the far left terminal.

Update 2:

This thermostat only deals with heat.

6 Answers

  • 1 month ago

    photo of the existing dial thermostat

    Attachment image
  • 1 month ago

    You have a line voltage thermostat.  

    Do not attempt to use a low voltage thermostat.  

    You need to get a programmable line voltage stat or a conversion kit to use low voltage stats.  

    I'm guessing you are in the UK.

  • 1 month ago

    It sounds like your old dial thermostat may be high voltage, and you're trying to replace it with a low voltage programmable thermostat. You'll need to check with a voltmeter to see what the voltage is on the old wires. When I replaced mine, I had to install a low voltage transformer and a 12 volt relay.

  • Anonymous
    1 month ago

    Check the instructions that came with the new thermostat.

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  • Droopy
    Lv 5
    1 month ago

    earth wire? is it green?  thats probably a fan control wire.  Your red is your 24v or millivolt wire.  And the black is probably your Heat wire.  Course this is all a geuss as different people/companies use different colors.  Like that black wire could be a common wire.  Without laying eyes on it is hard to tell. A picture would help.

  • 1 month ago

    the replacement comes with instructions -- if they are lost, see the maker's website.  Off hand, I'll hazard a guess [you didn't say] that this thermostat controls only the heat.

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