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Replacing thermostat connected to a ehc-Fusion boiler

Discussion in 'Plumbing and Central Heating' started by lt8480, 31 Jan 2018.

  1. lt8480

    lt8480

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    The boiler's circuit board is unlabelled, but based on the current configuration hope someone can help check my deductions/proposal...

    At the moment:

    Programmer/Timer (Sunvic Select 107XL)
    N/L connected to its own fused spur power supply.
    1/COM is connected with a Brown/Live cable to the Boiler
    3/ON is connected with a Brown/Live cable to a separate Thermostat's L connection.

    Dial Thermostat (Honeywell)
    L connected to programmer as above
    N connected to the Boiler with a Blue/Neutral cable.

    Boiler (EHC Fusion - Electric boiler running heating only)
    The connections are unlabelled, but the programmer and thermostat are connected as above. There is a large label above the circuit board that states "NA - Volt free control stat connections".
    (This circuit board does have some labelling but these are just holes and do not have connection blocks, they are labelled e.g. X1-PSK, X9-Tzas +/-, X8-Tco2, X7- etc.)

    Proposed:

    We have a new wireless programmable room thermostat (Salus RT510RF) to replace both the Dial Thermostat and the separate Programmer/Timer.

    The new programmer has the following connections NO, COM, L, N

    Based on the existing wiring to the boiler I understand the connections to this should be as follows:

    L/N to the fused spur
    COM to where the L/Brown cable currently connects.
    NO to where the N/Blue currently connects.

    Not that savvy on this, replaced a couple of Thermostats before but used to seeing labels on the boiler! - so if someone could check/confirm the above that would be great and all help much appreciated.
     
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  3. stem

    stem

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    Based on your description above, I have made a sketch below of how I understand the existing set up to be. Is this correct?

    Drawing1 Model (1).jpg

    If so, and if I understand...
    ...to be as below, then you are correct.

    Drawing1 Model (2).jpg
     
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  4. lt8480

    lt8480

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    Hi Stem, yes that's the correct (the ? in your first diagram is labelled N).

    Many thanks!
     
  5. stem

    stem

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    Are you sure it's actually marked N? A thermostat is just a switch. When 'on' both wires are connected together, 'off' and they are not. You would never connect a L & N together :eek:

    Some thermostats do have a N terminal for other purposes, but if there are only two wires to yours it won't have been used.

    Anyway, as it's coming out, it doesn't really matter.
     
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  6. lt8480

    lt8480

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    Just double checked and on the thermostat they are labelled 1 & 2... I must have mis-read my notes and reading the cable colours.

    Many thanks again.
     
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  7. lt8480

    lt8480

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    All sorted and working great.

    Thanks again!
     
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