Total amateur, want to install nest

Discussion in 'Electricians' Talk' started by David Knape, Feb 12, 2021.

  1. The Happy Builder

    The Happy Builder Screwfix Select

    So presumably the only controls on the oil boiler are the thermostat built into it and the time clock?
  2. David Knape

    David Knape New Member

    That's it, which was my initial question, is the timer basically just a switch with a basic pin timer on

    And can the nest link just connect at the wall and the actuall display sit in the living room and monitor the heat level (thernostat) or is my thinking on it wrong ? And cheers for the replies.
  3. Sparkielev

    Sparkielev Screwfix Select

    Am thinking the Nest e might work which is just a thermostat, it could replace the time clock
  4. The Happy Builder

    The Happy Builder Screwfix Select

    There would not be any hot water when the Nest turns the boiler off.

    The full upgrade to control heating and hot water requires making it a S-plan system with a two port valve to shut the flow from the boiler to the cylinder off and another to the control the heating, BUT these valve MUST NOT shut off the flow from the back boiler or else it will boil and possibly explode.

    To make it economical the boiler needs to be turned off when both the hot water and heating are satisfied otherwise it will burn oil keeping the boiler up to temperature when there's no demand. (Known as cycling).

    So the Nest needs to control both the heating and hot water.

    There's no way that this is a DIY job, you need a heating engineer, and possibly an electrician as well, to sort it out.
    Last edited: Feb 12, 2021
  5. MGW

    MGW Screwfix Select

    I have Nest working on a C Plan, however there are no instructions in the Nest box for wiring as a C Plan. But first there are three versions of C Plan and not even sure if that is what you have.

    Some can it gravity, some thermosyphon, the C Plan has no pump for domestic hot water, only for central heating, and in the main no motorised valves, although I have two so that is not always the case.

    Idea is the hot water storage tank is above the boiler and hot water raises, this diagram2-old.jpg is basic C Plan, however so you can use it for DHW in the summer some times there is a thermostat on the storage tank with hot coil, and so you can adjust the DHW to a lower temperature to central heating water some times it does have a motorised valve.

    The basic Nest wiring diagram for C Plan is this C-Plan_basic_Nest.jpg The contacts 456 are reverse to normal 5 is output to boiler, in nearly every other 5 is live supply. Because with Nest you can set boiler to run for just 1/2 hour, it resulted in being able to use oil in the summer, where the old timer the DHW would cost more to heat than with an immersion heater because the boiler cycled for so long, so for just my wife and I in summer boiler runs for 5 x 1/2 slots per week, and that gives us enough DHW.

    Winter I turn DHW off, and it just heats each time the central heating runs, there is no way to turn it off.

    I have a house and an annex below the house so have two pumps and two motorised valves to select house or annex, in the main annex is not heated. Pictures are always good, to be frank in hind sight and hind sight is easy I would have been better with Hive, but not going to change it now.
  6. The Happy Builder

    The Happy Builder Screwfix Select

    As @MGW says “Winter I turn DHW off, and it just heats each time the central heating runs, there is no way to turn it off.”

    Which is fine if the hot water cylinder is in the bathroom or somewhere else where it can basically just be treated as a big radiator that helps to heat your home.But if it is in the loft or somewhere else where it doesn’t warm a room all it goes is slow down the time to heat your home when you put the central heating on after you have been out and used more fuel.

Share This Page