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NEST Heat Link Wiring - Half a job

Discussion in 'Electrics UK' started by MWHG, 23 Aug 2017.

  1. MWHG

    MWHG

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    Afternoon All,

    I've been trawling threads and Google for help. We've recently had an extension built and a new boiler installed. On asking the plumber to install the Heat Link he stated not his job and on asking the electrician he stated the same. This went on until electrician agreed. Any how in trying to set up the thermostat the Heat Link was found but unable to control. On Investigating the electrician had only give the Heat Link power and not connected any boiler controls.
    It's a Baxi Duo Tec 33 and Nest 3rd Gen. I've attached some pictures and hoping someone could shed some light on which connections I need to make.

    Many Thanks
     

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  3. ericmark

    ericmark

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    Designing a homes heating system is likely the hardest thing to design in a modern house, the first point is of course the design of the house. I have lived in three homes, each one very different, two were controlled by thermostats, one was hot air so it did not matter where the thermostat was air circulated, the next was open plan, so again air circulated so again thermostat worked well, the last was a traditional house with doors on each room, and no vents in the doors, and thermostat radiator valves (TRV) in each room, they were also fitted in the open plan house to stop bedrooms over heating, but in the house with rooms and doors on every room each room is controlled independently.

    The plumbing system is designed for this, as each TRV closes then the return water gets warmer and warmer, likely lifting a by-pass valve and the boiler flame height reduces giving a seamless hysteresis free control. As it reaches the point where the boiler can't reduce flame height any more it starts to cycle, built in anti-cycle software reduces how often the boiler fires up to test the system, however it can't turn the boiler off.

    So now comes the hard bit, some how you need to turn off the boiler in the summer, so the options.
    1) Manual it's warm enough so you switch it all off.
    2) Fully automatic the TRV heads are replaced with electronic heads which in turn connect to a hub, when every head reports satisfied then the hub turns the boiler off.
    3) Some thing between the two, common idea is fit a thermostat in the coldest downstairs room, which also has no alternative heating, and no doors to the outside and don't fit a TRV to that room or turn it wide open.

    The problem with 3) is often there is no room to fit the bill.

    So one can understand why neither the electrician or the plumber wants to get involved, the plumber is simply a worker of lead, what plumbers do today not sure, as very few lead roofs or lead pipes, the pipe fitter is very skilled but these people work on 36 inch heavy walled pipes not little pipes up to 6 inch, I would say some one who does not work with lead, but uses plastic or copper is only semi-skilled.

    The gas man and the heating and ventilating engineer however have skills the old plumber did not need, but step one in every trade is design.

    So who designed the installation, and what did the designed ask the electrician and/or plumber to do? Many of an installation job I did not have a clue what the wires did, plans said run cable from A to B and connect wires to terminals UVWXYZ and that is what I did, some one latter came along and commissioned it.

    So in your case the thermostat may go direct to boiler, but it could also go to a motorised valve, and it could also go to a hub. Without knowing the system we can give totally wrong answers.
     
    Last edited: 24 Aug 2017
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  4. MWHG

    MWHG

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    Thanks for taking time to reply EricMark. Any idea on the wiring for Heatlink to Baxi Boiler?
     
  5. ericmark

    ericmark

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    The yellow link wire would normally go to switching device. It states 230 volt so the device needs to be rated at that voltage. For the I found this PDF however this shows one relay contact your picture shows two so I would assume yours also does hot water?

    I looked into the idea of Nest and I must agree the instructions do seem to leave something to be desired, I found this [​IMG] which seems to show terminals 2 and 3 would replace the yellow link wire, and T1 and T2 goes to thermostat. If the unit does not do the hot water, however if it does do hot water then the terminal 2 and 3 will likely go to a motorised valve for heating and 5 and 6 to the motorised valve for domestic water heating.

    In fact often not as simple as that, job one is to work out which plan it follows, we have a selection of plans like W and Y most written by Honeywell and followed by most electricians and plumbers, some give priority and some simply share. I am guessing since yellow link in place you have not got domestic hot water from the central heating?

    There are other methods but since we are really all in the dark as to what you have best option is only a guess.
     
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  6. stem

    stem

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    The Baxi Duo Tec's I have seen have all been combi boilers, so if yours is a combi also, then the Nest Heatlink hot water terminals 4, 5 & 6 will not be used.

    Then as ericmark says remove the yellow loop between the boiler terminals 1 and 2.

    Connect boiler terminal 1 (Switched live in) to the nest terminal 3 (Heating call for heat)

    Connect boiler terminal 2 (230v live out) to the nest terminal 2 (Heating common)

    As there are no connections made to T1 & T2 at the Heatlink, the remote Nest Thermostat will need to be powered via its own separate plug in power supply.
     
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  7. MWHG

    MWHG

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    Stem / EricMark - Many thanks for your answers. I wired up the Heatlink last night and the Nest thermostat now controls the boiler...:)
     
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  8. DIYnot Local

    DIYnot Local

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