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Internal doors open or closed effect on central heating.

Discussion in 'Plumbing and Central Heating' started by ericmark, 6 Nov 2020.

  1. ericmark

    ericmark

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    Location:
    Llanfair Caereinion, Nr Welshpool
    Country:
    United Kingdom
    I look at Nest as I pass and Orange, so boiler activated, but can't hear boiler running, the Gen 3 wall thermostat is in about the most central place in the house, but room temperatures are controlled by nine programmable TRV heads, but the oil boiler is a fixed output so cycles off/on as required, but it must cost to heat the pipe work, and if all TRV are closed then pump sucking on a closed system which will likely cause cavitation so can't be good.

    I asked for a by-pass valve to be fitted, but seems it will not work with pumps on the return, it is a C plan with DHW thermo syphon no tank thermostat or any motorised valve on DHW.

    So if house is satisfied then would be good if pump stopped.

    It would seem previous owners did not use central heating, they simply lit a fire, as the central heating was in a mess, they had fitted two pumps, one for main house and one for flat under the house, the flat one was worked by flat thermostat, but main house we had to walk outside down a flight of steps and plug in the pump, and there was no main house thermostat that we could find, found the receiver in the flat, but no thermostat.

    On trying to use I found using one pump it would push water in reverse direction on the other system, but with much reduced flow rate, so I could not turn off the flat central heating, and use main house only, or turn off main house and use flat only, so I got a heating engineer to fit two motorised valves, I had expected it to then use one pump, but no, two pumps still fitted, so need a relay with pump to turn on boiler.

    Found the main problem was the triple and earth cable main house to flat which should have turned on central heating or DHW changed colours red, yellow, blue to brown, black, grey and one core not connected, seems likely some junction box hidden behind plaster board in flat, so swapped supply from house to flat, and used the two good wires to power Nest Gen 3 in house, so only 12 volt to where ever the junction is. Seemed safer that way.

    So the two wires now can control CH and DHW and power the Nest wall thermostat. I brought 4 Energenie TRV heads from old house, and added 5 eQ-3 heads for upstairs and kitchen, and they work well, the boiler does trip out every so often, but other than that is works well, and the boiler will stop once water is hot enough, but that leaves the pump running, likely the TRV heads never fully close so likely still some circulation, there are 14 TRV's in total, although 4 are in flat so not used, yes bathroom towel rail has no TRV but that is thermo syphon so does not really help.

    So want the hall wall thermostat to detect when house is warm, and turn off heating, so should I leave doors open or closed on entrance level rooms?
     
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  3. Terrywookfit

    Terrywookfit

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    Close doors and remove trv in room with stat fitted.
    If rads are correctly sized the rooms should reach temperature.
     
  4. ericmark

    ericmark

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    Location:
    Llanfair Caereinion, Nr Welshpool
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    I found out why the pump was running without boiler, the boiler had tripped yet again. That was my worry that pump running the TRV's are all closed. To remove or set the TRV to a higher temperature to the wall thermostat has been tried, it does not work, the hall temperature grossly over shoots and the the wall thermostat turns off for an extended time, so get a massive hysteresis.

    I know the TRV has to actually be set lower than wall thermostat to prevent hysteresis.

    At the moment the hall thermostat shows 19°C and is set to 19°C and the TRV shows 18°C and set at 20°C this is normal the TRV always shows a degree or two less than the wall thermostat, and the anti-hysteresis software in the TRV means when set at 20°C it starts closing at 18°C, I found in last house with a modulating boiler I had to cheat, and set in morning to 22°C for an hour then back to 20°C or from 7 am it would take to 11 am to get room to temperature, but if I cheated as set to 22°C for and hour then back down, by 8 am it was at 20°C and it stayed there all day +/- 0.5°C.

    The programmable TRV heads are good, however not quite so good in this house, mainly due to the wall thermostat turning boiler off for an extended time, clearly the TRV can only warm a room if the water is warm and circulating, and unlike the modulating boiler, this boiler turns off/on on a mark space ratio to regulate water temperature, and the wall thermostat does the same, but the time mark plus space is too long, the mark + space needs to be less than an hour or the radiators have gone cold, so all the TRV's have opened and on restart all radiators get warm, and any room which has not cooled that much then over shoots, some control is possible with the lock shield valves, but once running the TRV's should control temperature not the amount of throttling of the lock shield, or on temperature charge in the room, it can't catch up, radiator will not reach full heat because of lock shield.

    As said today's problem was the boiler tripping, but on normal running the wall thermostat increases temperature at 0.5°C per hour, so the TRV's can control room temperature, because of the trip the wall thermostat has risen by 1.5°C and so over shooting has happened and my bedroom is cool as a result.

    So I wonder if the doors being chocked open on entrance level will reduce the hysteresis? Or may be just one of the 4 doors, could turn up the TRV the only one not programmable on the shower/toilet room so wall thermostat gets heat from both sides?
     
  5. DIYnot Local

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