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Honeywell System Issue

Discussion in 'Plumbing and Central Heating' started by Gavin Jones, 29 Dec 2020.

  1. ianmcd

    ianmcd

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    Or the synchron motor has seized :rolleyes:
     
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  3. Gavin Jones

    Gavin Jones

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    Hi,

    so last night to get the house to cool down I turned off the heating and left the hot water on which worked. This morning I tried to move the switch and met resistance, when I let go the lever moved back to middle position but last night there was no resistance, does that help at all?
     
  4. CBW

    CBW

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    Mid position - suggests it’s letting by if selected hot water only.
     
  5. Gavin Jones

    Gavin Jones

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    I think at that point the hot water and heating was on
     
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  6. ericmark

    ericmark

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    Summer I would suspect the valve, but winter unless one of the thermostats calls for heat, then boiler will not run, it does not matter if valve open or closed, unlike the S Plan where a stuck micro switch can cause boiler to fire, if the thermostats are off although the grey wire is powered, there are resistors and diodes between then line feed and orange to boiler, so even if micro switches stick, can't see how with the plan shown the boiler can be powered.

    To get 3°C over the setting is possible due to over shoot, I get that in this house, so showing 23°C is possible with nothing wrong, when set to 20°C but not 23°C with boiler running when set to 20°C. There are with some Honeywell thermostats built in anti-hysteresis, not sure with one you have, and with anti-hysteresis as it approaches the target temperature it starts to cycle off/on gradually increasing the off time. Today this is bad for modern gas boilers, great for oil, but gas boilers modulate (turn down) so this method is now now very good so modern thermostats work out the over shoot and stop early, the so called "Smart" thermostat, this is what Nest does in on/off connection, simpler thermostats use wireless links to the TRV heads, and don't have built in algorithms, this is how Hive works.

    So in theory even if the thermostat goes faulty and powers the boiler 24/7, the room should not over heat as the TRV will cut in and reduce flow in the radiator. With non wireless linked TRV heads they can only stop over heating, you need a wireless link as with Hive to turn on the wall thermostat, so the way Hive works, you could set the thermostat to 16°C but it heat the room to 23°C because of the TRV setting, as the Hive TRV head sends a "demand for heat" to wall thermostat so switches on boiler even when wall thermostat is satisfied.

    I don't think your thermostat has links to TRV heads, so it sounds as if faulty, but in essence with modern boiler, the wall thermostat can have many jobs, from turning off the boiler when warm weather arrives, to connecting to boiler ebus and controlling boiler output, the old idea of not fitting TRV heads to room with the wall thermostat often does not work, specially where in the hall, so want fast recovery when front door opened.

    The modern gas boiler (not oil) can what they call modulate, that means it can turn down the flame height. There are two ways it can do this, special thermostat connected to ebus, or the temperature of the return hot water, as the TRV heads close the by-pass valve opens, so uncooled water returns to the boiler, when the boiler detects this hot water it turns down the output so boiler output matches demand, also it means the boiler gains the latent heat so works more efficient. If instead of using the TRV we use a wall thermostat it will still heat the room, but not as efficiently as to if boiler allowed to modulate as it is designed to do. So the on/off thermostat is set so it only works when we have a warm day.

    In my house we have oil, so boiler does not modulate but uses a mark/space ratio, so it does not really matter if the wall thermostat or the TRV controls the boiler, either will work, it is only with condensate producing gas boilers where it matters.

    However the point is even if the wall thermostat is faulty, the TRV should stop room over heating, mine are in fact too good, the anti-hysteresis software built into my Energenie electronic TRV heads is OTT, and set to 20°C it would take hours to get room to 20°C, so I set them to 22°C for an hour then back down to 20°C. Seems the Drayton electronic heads are "Smart" and work out when to shut, however the problem with "Smart" thermostats is one "Smart" device can upset another "Smart" device, also leaving doors open or closed also affects how the work.

    For central heating "Smart" means it works out how the room heats, connecting to a phone does not make is "Smart" Hive is not "Smart" it only has telemetry, Nest is "Smart". Not sure if Smart helps, it does not help in my house, as the Energenie TRV heads should work with Nest but don't.
     
  7. ianmcd

    ianmcd

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    The manual lever is there simply for filling the sytem with water when drained or first installed, with no demand for anything the valve will spring return to the HW only position, moving the lever with a demand for anything will tell you nothing
     
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