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Thread: Fitting Digistat +3

  1. #1
    Automated Home Lurker
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    Default Fitting Digistat +3

    Hi
    Just fitted a Digistat +3, replacing a mechanical Thermostat. Fitted the live Red wire to C, and the yellow to ON, and if I have read the diagram right then just isolated the blue wire which was fitted before as neutrual, and the OFF terminal is left blank. Im sure this is correct, but if someone could please confirm?
    The heating seems to work correctly, but the boiler is sometimes coming on even when all the settings are off . I dont think it has anything to do with the new room stat, but can anyone advise.
    Cheers

  2. #2
    Automated Home Sr Member NeilUK's Avatar
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    Most modern digital thermostats do not use or require the neutral connection so making the blue wire safe (wire it into a terminal strip left in the back box) will be fine. This does assume that the blue wire was used as a neutral and not some other signal wire. If you have a conventional heating system using 2 2-port zone valves (one for heating and one for hot water) then there is no need for the "off" signal to be wired. If you have a 3-port mid-position valve then you may well need this to make the valve work correctly. That said it my be that your timeclock/programmer provides this "heating off" signal in any case.

  3. #3
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    Thanks Neil.
    I'm sure it is wired correctly, and you have confirmed what I thought. I just can't understand why the boiler is coming on occasionally.
    If I set the programmer to have the heating and water settings to off, the boiler will still come on occasionally, stay on for a while and then go off. The pump isn't on and so all it is doing is firing up for a while then going off. It has me confused.

  4. #4
    Automated Home Guru MichaelD's Avatar
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    Is it a combi boiler with a small hot water tank built-in? Bosch and others have this facility so that hot water gets to the tap quickly, because there is some already heated.

    If so, then you will see the boiler coming on occasionally to keep the tank hot. There should be an eco option to switch this off

  5. #5
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    It's a standard boiler and have now found the problem. The clock was signaling for hot water all the time. Replaced the clock it is all fine.

  6. #6
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    One other question on the Digistat. It has an Intelligent delayed start option. To me I read this that if I select this option and set the temp at say 20 deg for 7:00am it would bring the heating on earlier than 7:00, so that it is 20 deg at 7:00? The time it brings the heating on varies depending on how cold it is.
    Having selected this option the heating is still not coming on until 7:00, what ever the temp.
    Anyone any advise, or have I just misinterpreted this option?

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