Advice on swapping honeywell programmer to Hive

Discussion in 'Electrics UK' started by gwebstech, 24 Nov 2021.

  1. gwebstech

    gwebstech

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    Hi all

    Im hoping to swap my boiler for a combi and in the process ill get rid of the honeywell programmer wired just below the boiler and swap it for a Hive thermostat, wireless in the front room.

    My question is: the programmer has loads of wiring going into it, as long as the boiler will be fed from id guess a fused spur, what about all the other wiring to the programmer? Weve got a hot water tank upstairs so im assuming that once thats gone, the sparky or plumbing engineer will be able to disconnect the wires so i can tile over where the programmer was?

    Anyone know if the Hive works ok doing this? i think Nest has to be wired doesnt it?

    thanks

    Gaz
     
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  3. flameport

    flameport

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    If you must go for a combi, then all of the wiring goes away as well.
    All you will have is a 3 core flex supplying 230V to the boiler, and another flex (5 core usually) to the Hive / Nest / other receiver unit which would be located next to the boiler.

    The actual thermostat device is wireless, and can be located anywhere. Some have a desk stand it can fit into, or wall mounted. Some use batteries, others a USB adaptor.
     
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  4. gwebstech

    gwebstech

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    thanks for the reply mate, im partly going for a combi to free up thecupboard in the bathroom - need the space.

    Im going for the hive as as far as i know, its wireless, the house i just sold had Nest and they were wired to the boiler, can do that here without making holes in walls etc
     
  5. ericmark

    ericmark

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    Gas or oil? Will the boiler be OpenTherm enabled? How much are you willing to spend? And many more questions.

    It depends on your house, most central heating system are a compromise.
     
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  6. stem

    stem

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    Might be worth bearing in mind, that when gas / oil boilers are outlawed, and if we are are all forced to use heat pumps, you will need to reinstate a hot water storage tank. Current heat pumps can't produce the heat required to provide the instantaneous hot water like a combi can.
     
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  7. ericmark

    ericmark

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    This is the bit I looked at, as I said a compromise, but if gas then likely modulating, i.e. variable output, likely between 6 and 28 kW and this is done in the main so the return water is cool enough for the boiler to extract the latent heat from flue gases.

    So with a modulating wall thermostat in the main room, this is possible, but Hive does not modulate. Whole idea of Hive is control is by the TRV heads but there is a upper limit of 22°C for the wall thermostat, above this limit it will not accept any demands for heat. So the on/off wall thermostat is placed in a room with no alternative heating, on the lower floor, with no outside door and normally kept cool, often no such room so hall is often used, its job is to stop boiler cycling in the summer, Hive is a little more flexible as it can accept a call for heat from linked TRV heads unless at 22°C or over, but the wall thermostat is still there to switch off whole heating system to stop cycling or if geofencing is enabled when your not at home.

    With oil where the boiler does not modulate maybe on/off thermostat is fitted in main room, but with gas only if using a modulating thermostat.

    When you turn off a boiler any heat in boiler is lost out of the flue, and when turned on with on/off thermostat or programmer it starts at maximum output, so boiler gets hot quick, if turned on by the boiler as return water cools then turns on at minimum output, same if turned on by a modulating thermostat.

    So idea is to avoid on/off switching as much as possible, clearly turns off when you leave house or go to bed, but each time is switches off the boilers internal system is reset. So the TRV is king, since the TRV turns up/down rather than on/off it does two things, one it allows the boiler to run more economical, and two it reduces the hysteresis to a minimum.

    The problem with non linked TRV control is it can't turn the boiler on, so we select key rooms to be linked.

    The problem is so often central heating is not set up. The hard bit is setting of the lock shield valve, closed too far and room will not get warm enough, everyone understands that, but open too far and the boiler gets hot water returned premature, and the TRV can't close fast enough to stop a hysteresis starting, normally start setting is around 15°C drop feed to return on radiator.

    To my mind biggest problem is TRV marked *123456 we know we want say 20°C but we have no idea if that equals 2 or 4, and in real terms there is no exact number that = 20°C likely around 2.5 but depends on room size and radiator size. If you take a standard TRV and try blowing through it, at 20°C you will realise it starts to close at around 4 and fully closed at 2 it is an analogue device.

    With electronic TRV heads even the cheap ones at £15 each 61dmtMm13BL.jpg it shows °C. This means you know setting on TRV so now it is simple, if temperature over shoots you close the lock shield valve a small amount, and repeat until it does not over shoot. You only have one variable. Once lock shield set you could return to old type TRV and these work great, unless you want a programmed change, but you need one set correct so you can set the other.
     
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  9. gwebstech

    gwebstech

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    Hive wont call for heat above 22? thats no good for er indoors, jesus. Doesnt need to be hive, i bet honeywell or ismilar do a decent same type of thing.

    So are you saying ill need all new TRV tht can coommunicate to the thermostat?
     
  10. crystal ball

    crystal ball

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    My Hive goes up to 32, works well without TRVs
     
  11. ericmark

    ericmark

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    The Hive wall thermostat will only accept a call for heat if under 22°C.
    So with no TRV's what would make a call for heat?
    Whole idea is if a room with a linked TRV head wants more heat even if the wall thermostat is set below heat of room, it will fire up the boiler for ½ hour to allow the room with the linked TRV head to catch up.

    If Hive in hall all other room could be set at 24°C as long as hall does not exceed 22°C.

    Be it EvoHome EVO-home1.jpg or Wiser Drayton1.jpg or Tado each have there own plus and minus features. Main point is the TRV controls the room, the wall thermostat or hub just collects the information and decides what to do with the boiler. Within the limits of the boiler software, and the way it can interface with thermostat software.
     
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  12. flameport

    flameport

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    Not true.

    You do not.

    There is an option to install a cable from the receiver unit to the Nest thermostat to provide 12V power for situations where it will be permanently wall mounted.
    It's not necessary, as the thermostat can be used with a desk stand and a USB cable.
     
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  13. ericmark

    ericmark

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    I was unaware of the limit until about 3 weeks ago, and it seems likely to be made user settable in the future, but the 22°C is the limit at which the "demand for heat" system which links the TRV to the wall thermostat stops working, not the wall thermostat as a whole stops working.

    I have myself failed to set TRV heads correctly, in my mothers house I used a wall/free standing thermostat IMGP7319_20_21_tonemapped.jpg with the idea the living room was important and it did not really matter what happened to the bedroom, hall, kitchen etc, as long as not freezing.

    What I failed to do however was also set the living room radiators TRV and lock shield valves, and the wireless link was lost to thermostat shown, so walked into her living room and the heat hit one at 32°C which should have never happened even with a faulty thermostat.

    After this event I did take some time and effort to set the TRV and lock shield valves, and actually fitted an electronic TRV head.

    But we all make mistakes, and I can see how a limit of 22°C for the "demand for heat" system is a good fail safe, specially where some one has not fitted a TRV in the room where the wall thermostat is fitted.

    This house I also have a problem, most homes the hall cools reasonable fast, so a wall thermostat in the hall to turn off heating works well. But we can control speed of heating with the lock shield valve, what I can't control is speed of cooling, so hall heats to 19°C at 0.5°C every two hours from 17°C so it takes 8 hours to raise 2°C and boiler fires at least 4 times, ensuring rest of house warms up as the programmable TRV heads are set for it to do.

    But by 6 pm the hall is warm enough to switch off boiler and it does not cool fast enough, so living room cools before the hall, my cure is to leave kitchen door to hall open to cool hall, or failing that dinning room door, want living room at 22°C so need that door closed.

    What I want are these upload_2021-11-26_9-31-3.png temperature sensors that link to my main Nest Gen 3 thermostat, but as yet not released in UK, this is where Hive works better than Nest, Hive also had the problem but they released the Hive TRV head upload_2021-11-26_9-42-29.png which links to the wall thermostat with the demand for heat system. Had I used Hive I would not have any problems, but when I fitted Nest the Hive TRV had not been released and Nest worked with Energenie Mihome TRV heads, so at the time of buying Nest was the best of the two.

    But due to the way Hive works, in the main best location is the hall for the wall thermostat. Very few people want the hall at 22°C we want to set the wall thermostat so the boiler only turns off when either there is a program change, or a warm day, the TRV is analogue it gradually opens or closes, and the boiler is analogue (with gas) so it also slowly turns up or down, so working together you get a hysteresis free control of the home heating.

    But when warm weather returns the TRV does not have the ability to turn the boiler fully off, so boiler would cycle all summer, so the wall thermostat is required to turn off boiler in the summer.
     
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