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Replacing old analog with digital room thermostat

Discussion in 'Electrics UK' started by styoda, 4 Dec 2019.

  1. styoda

    styoda

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    Hi All,

    I'm planning on changing the old analogue thermostat to a newer digital one and would like some confirmation if this can be done.

    At the moment I have an old Honeywell ST699 programmer and not sure what the thermostat is, it's looks so old and doesn't work properly.
    I would like to replace the thermostat with something like a Honeywell CM907, which has more timer options, which I need.

    To get the CM907 to work with the ST699, if possible, would I have to set the heating on the ST699 to continuous and then just program the CM907 to switch it on at the right temperature ?

    Any help would be greatly appreciated.

    Thanks
     
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  3. AndyPRK

    AndyPRK

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    That’s correct.

    The old timer can be useful for providing the twice daily and once function if sometimes you are home all day and other times at work
     
  4. styoda

    styoda

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    Thanks very much Andy, that great.
     
  5. ericmark

    ericmark

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    Modern analogue thermostats are far better than digital if the boiler supports them, both can have analogue or digital human machine interface (HMI) it's the way it controls boiler, either on/off (digital) or up/down (analogue).

    Today there are two completely different types of boiler, old or oil simply switch on/off, new gas turn up/ down or modulate. There are two basic methods to control the boiler modulation, connection to ebus, or with the temperature of the return water.

    In both cases the TRV (thermostatic radiator valve) is the key component, a number of methods are used to combine the wall thermostat and the TRV, from electronic heads to controlling one room which is set to take longer than rest of the rooms to heat up.

    So complex thermostats like EvoHome, Nest, Hive and Tado or programmable thermostats with the TRV program set to match, or simple heating on/off.

    So most of us use a middle road, however if you want to up grade, step one is decide final aim even if going to take 5 years but you don't want to buy things twice.

    I will admit I got it wrong, I bought 4 wifi TRV heads and fitted in old house with idea of adding Nest latter, on moving took heads with me, and added Nest, only to find Nest no longer support MiHome TRV heads. They still work, but not integrated have to set TRV and wall thermostat independent.

    So a cheap £10 electronic head would have done same job. And most programmable wall thermostats today have at least three setting through the day. So hard wired programmable thermostats start at around £35 so can be done quite cheap.

    Wireless thermostats are more of a problem as cheap one don't fail safe, so with discharged batteries they can leave boiler on.

    But decide final aim, then get bit at a time, and I started with programmable TRV heads which still seems way to go.
     
  6. AndyPRK

    AndyPRK

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    If the batteries fail and the hearing was on I’m happy for it to stay on!

    Don’t want to be cold waiting to buy new batteries !

    Can always shut off boiler if roasting.
     
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  8. ericmark

    ericmark

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    For years I used a Horstmann DRT2 thermostat, swapping batteries every years it worked great, they would last around two years, so swap every year and fine, if batteries did become discharged it would default off, only problem the depleted battery sign comes on after the point where it stops working, so needed wireless with mothers house so got a Horstmann HRFS1 however this was a problem it would miss the change and both stick on and off, it would not then switch on/off without turning the heat up/down.
    The DRT2 was replaced with Flomasta 22199SX which was nearly the same, but extra on/off per day, and can be set default on or default off, the HRFS1 was returned to the Honeywell Y6630D wireless thermostat which default is off, and the batteries lasted around 3 to 4 years, and it always failed off with either flat batteries or anything that messed up RF signal, if no signal every ½ hour it turned off, it also had anti-hysteresis software so as it approached set temperature it started a mark/space ratio so temperature did not over shoot, it had an analogue dial and was not programmable, but was a very good thermostat.
    New house using Nest Gen 3 it will work wireless and you can select digital or analogue connection to boiler, I am using analogue as oil fired and also using hard wired connection option, the dial is same idea as computer mouse, so really digital but it looks like analogue, and has a digital display which you can select what it shows, temperature, time, date etc.
    As to use with phone, did not set geofencing but found it was auto set, so does auto turn down temperature when I leave the house, however also using Energenie MiHome TRV heads on entrance floor and they also can have geofencing set, but also have anti-hysteresis software which means they take a long time to reach set temperature.
    Position matters, 6 am at moment bedroom at 19°C living room 16°C and hall where main thermostat is, 16°C on the TRV but 17°C on wall thermostat, the latter closer to centre of house and higher up. Old house on a sunny morning measured as much as 8°C difference in the same room, depending on if sun hit the area, how close to radiator and if door open or closed TRV would show 20°C but weather station would show 28°C out of direct sun light but near window, in sunlight hitting 32°C. All the instructions show wall thermostat on wall opposite the radiator, if the radiator is on an outside wall this works, but if on inside wall that means thermostat on outside wall so always registered low as wall cools it, with the HRFS1 we could move it, best position was found on a tea trolley 2 foot from radiator, and once we went to electronic TRV heads they were the best control we have every had.
    This house the wall thermostat is poorly placed, but since Nest which predicts it still works well.
     
  9. Mottie

    Mottie

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    I hate your rushed partial answers. :rolleyes:
     
  10. AndyPRK

    AndyPRK

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    There is an ignore button.
     
  11. Mottie

    Mottie

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    73EE3C85-8012-498A-A678-24B68E4B4961.gif
     
  12. AndyPRK

    AndyPRK

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    I know it was Sarsasm.

    But if you don’t want to read a load of text.... press the button
     
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