Thermostat receiver query

Discussion in 'Electricians' Talk' started by Tilt, Sep 22, 2022.

  1. Tilt

    Tilt Screwfix Select

    My room stat can be showing a good few degrees below it's 'on' setting temp, so I would expect it's receiver to remain switched on ....... so just awaiting a command from the boiler.

    Any reason why it (the receiver) still switches in and out randomly????? This is without any room temp change and prior to anything being turned on.

    The whole installation is a little under two years old and generally works fine but sometimes I come home and switch the boiler on but it does not come on straight away as the receiver is switched off (it has a green indicator light on it when it is on)
    It can be a few minutes (maybe slightly longer) before it switches the boiler on.

    I am talking strictly central heating control.

    It is Honeywell kit Y9240S1005 although the receiver is a bit different to the one showing in my old screwfix catalogue. (I will double check this item)
    It is this one.

    Thank you.
    Last edited: Sep 22, 2022
  2. quasar9

    quasar9 Screwfix Select

    Some CH boilers take a few minutes to get going. Often they do weird things like purging the exhaust, get the pump running etc, before they fire up. But the green light on receiver should come on immediately on command from the thermostat transmitter
  3. Notnowvicar

    Notnowvicar Active Member

    If you download the manual you will find that there is a few choices...cycle frequence - how often the boiler cycles when a temp that is set starts the boiler, ie it waits a period to see if the room temp goes back up after it gets a low temp reading. say when a door opens and air flows, it waits to see if the heat in a rad warms the space back up. Eco seems to do a range mode that also allows for a wait state before firing....the maanual I found was for eastern europe with english enjoy
  4. MGW

    MGW Screwfix Select

    I think that thermostat has hysteresis software, so as it approaches the set temperature it starts using a mark/space ratio so it does not over shoot and the same as temperature starts to drop.

    This is not really very good with a modulating boiler, but very good with an on/off boiler.
    NewMaldenBoy likes this.
  5. NewMaldenBoy

    NewMaldenBoy New Member

    I am sure the honeywell has give and take built in so there is a lag on boiler startup and also switch off
  6. MGW

    MGW Screwfix Select

    Sorry was a quick answer, my mother had this 84067_P.jpg thermostat which did the same thing. With a gas modulating boiler the room thermostats look some thing like this, EQ-3 Bluetooth Smart Radiator Thermostat.jpg and they communicate with the boiler using the return water temperature, and don't switch on/off but the motor slowly adjusts the flow to maintain the room at the selected temperature.

    However they have a problem, they can't turn the boiler fully off, it has to cycle on/off to see if heat is required, so we want a wall thermostat which will turn off the boiler in warm weather and turn it back on when the weather cools, and likely a very simple bi-metallic strip type does a better job to an electronic type.

    However this assumes we want heat 24/7, and in the main we don't, so the TRV head shown is programmable so only heats when required, but we want the wall thermostat to either do the same, or to act as a hub and be linked to the TRV's.

    The TRV head shown cost me £15 each, but a linked TRV head costs more like £50 each. So we are now looking at cost, so this upload_2022-9-23_10-23-59.png programmable thermostat is good enough to follow the same schedule as the TRV heads at £35 approx, so bargain basement say 6 x eQ-3 heads and a wall thermostat starts at around £150 to get reasonable control of the central heating, but it does need to lock shield valves to be carefully set.

    We can compare that with the likes of Drayton Wiser or Honeywell Evohome which are clearly better, but with a massive price hike by time you buy the TRV heads.

    What the first question has to be, is how the thermostat links to the boiler, it can be simple on/off or it can actually modulate the boilers output with in the main OpenTherm.

    The question has been asked many times, how much does having an OpenTherm system save, and can't seem to find the answers, clearly the price of oil and gas has gone up, but until this year I was looking at around £350 for oil, and a super system may save 10% so £35 a year, so spending £1000 on control would take more than my life time to get back.

    When I was about 20 years old I saw the first central heating systems being installed in homes, the early ones only ran morning and evening with a programmer, then we saw the TRV, and slowly over the years more and more control, but we have only been using central heating for around 50 years, and most the old stuff is now redundant. So we are likely looking at 15 years max pay back time. By then we will have some thing new, so paying £200 to improve the system yes, but over that unlikely it will pay for its self.

    Like the Energy certificates for the house, where it says under floor insulation fitting costs £5000 gain £30 a year, why even list it? But LED lighting £100 gain £20 a year clearly worth while.
  7. Tilt

    Tilt Screwfix Select

    Thanks for the replies so far guys.
    The question is not about having the boiler on or anything to do with the boiler really......
    It was purely about the random switching of the wireless receiver.

    It was a little difficult to explain the situation easily but this random switching on and off of the receiver is happening even when the heating timer is OFF and has been OFF for days.

    I would have assumed that the receiver would remain with it's green light on (assuming the room (the room with the thermostat in it) temperature was well below the thermostat temp setting).

    I never thought of checking if it randomly switched during the hot weather.
  8. MGW

    MGW Screwfix Select

    I had the same with mine, in my case Nest Gen 3, it seems it was an anti legionnaires thing and it ran the boiler at some odd times, however found it could be disabled.

    Likely due to English used, what is a system boiler? Seems non self contained, although seems not the only thing, high integrity consumer unit, who thought up that description. However due to English used seems I set it up wrong.
  9. Notnowvicar

    Notnowvicar Active Member

    If you check the manual you will find that whilst the thermostat is bonded to the receiver it does not communicate to it all the time to save just calls mama from time to time. Its right there in the could read that yourself.
    Tilt likes this.
  10. Tilt

    Tilt Screwfix Select

    @Notnowvicar Appreciate that ^^^ and the link bud......

    I am looking into a different way of monitoring what or when it is happening.
    I have moved the thermostat to a considerably colder environment and I think the receiver light does stay on (need a little more monitoring to confirm this).

    So this
    similar to this
    make reasonable sense. Though for sure, it seems to happen at least a degree or two lower than I would have thought.
    @Notnowvicar I will read the manual when I get around to it one day, so thanks.

    One thing that I hadn't thought of before is the fact that the receiver would be unaware HOW any room (that stat is in) temp changes are happening.
    ie it could be the weather OR the boiler could be running the heating.

    So even though the receiver is sending a signal to the boiler, it still doesn't know if the boiler is actually running or not.....

    Thanks guys.

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