Getting my head around central heating controls.

Discussion in 'Plumbers' Talk' started by MGW, Nov 8, 2018.

  1. MGW

    MGW Well-Known Member

    I have a problem with rooms too hot, so tried swapping the wax heads in the TRV's (Honeywell VT15) to electronic, adjusting lock shield valves, and wall thermostat improved but still not right.

    However there is one control I have never touched, the radiator water temperature control on the Worcester Bosch Greenstar boiler, maybe this can help?

    What I am guessing is with the thermostat in hall turning on/off (Honeywell Y6630D) the TRV heads (Energenie MiHome) are opening too much then can't close quick enough so radiator over shoots? Hence tried to slow radiators heating using lock shield which are on the feed side of radiators.

    So slowing down how quick the room heats may help? There must be a reason why we are allowed to alter water temperature, clearly the hotter the water the more heat radiated, but not sure what else it does, some insight please.
  2. chippie244

    chippie244 Well-Known Member

    My central heating is thus, wife gets up and puts fluffy dressing gown on and goes down stairs and turns the heating on, I get up later and it's warm, as I leave the house I turn the heating off.
    Wife comes home, turns the heating on and puts her fluffy dressing gown on, I get home and it's warm..
    Wife goes to bed and turns heating down.
    I go to bed and turn heating off.
    No trv's, no hive. no nest, no problem.
    If it's cold then put a jumper on.
    seneca, Peter208 and Heat like this.
  3. Heat

    Heat Well-Known Member

    Sounds like you only have mechanical controls.
    Fingers to work the buttons and legs to get there. :)
  4. Heat

    Heat Well-Known Member

    The hotter the water in a heating system, the higher the output of each radiator.
    Also the radiators will be quicker to get a room up to whatever temperature desired.
    Altering the lockshield rad valves is not a good idea. They really need set for to solely give a balanced flow throughout the system.
    It might be more a design problem with the system.
    The zone stat is critical to be in a zone that similarly heats like rest of home, plus it needs set at a correct temperature, which might need a bit of experimentation.
    Your hall rad(s) where you have the wall stat may not be of an output size equivalent to other rooms, for example. In other words, hall rads could be undersized in comparison to some rooms.
    But your radiators TRVs should be controlling each rooms heat fairly well, if each are set at a proper heat for each room.
    I find folk tend to turn TRVs to highest or close to highest settings
  5. MGW

    MGW Well-Known Member

    When I first looked at heating in this house every lock shield valve was fully open and some rooms never got warm, which at that time included mothers bedroom.

    So I went around roughly closing lock shield valves to get flow in the rooms furthest from boiler.

    The hall radiator is massive, clearly to re-heat hall quickly after front door has been open, the lock shield valve setting in hall however I had set low, or all other rooms would get cold, so when front door was opened it did not re-heat very quickly as lock shield valve turned down.

    So I added a TRV to hall radiator, that was the biggest improvement made, it took some setting up to start with, but careful trimming of that TRV and opening of lock shield valve means that opening the front door I get a rapid recovery until around 3°C of wall thermostat setting then it slowed down. This was further improved when an electronic head was added, now the hall recovers to 1°C of target then takes ages to gain that last 1°C which ensures boiler runs long enough to heat rest of house.
    Not sure what the highest setting is, I think around 32°C however surely no one would want a room that hot, depending on time of day my TRV's are set between 16°C and 22°C I set living room at 16°C over night so the valve will not be wide open when the programmer switches on the boiler, it is set to 19°C during day and 21°C in the evening.

    In case we get a really cold night, there is a second programmable thermostat in the kitchen, set around 16°C over night should it be very cold this thermostat in parallel with main one and programmer will cut in, for some unknown reason no frost stat was fitted in the house, it is also set for 20°C first thing in morning to extend the boiler run time in morning to allow rooms to re-heat to day temperatures, but then is set to 12°C for rest of day so has no effect during the day, mainly as too near to back door and mounted on oven so no good once we get up.

    There is to my mind not point in spending out on programmable electronic TRV heads and then not using them to individually control each room, the problem is leaving a door open heat from one area will bleed into another, so leave the living room door open and the heat from living room enters the hall and turns off the whole of the central heating as the master wall thermostat is in the hall.

    Being up or down 1°C is OK, however wife's bedroom often up so 3 or 4°C from setting on TRV electronic head, I have been scratching my head wondering why.
    1) TRV head faulty (Energenie MiHome).
    2) TRV base faulty.
    3) Flow wrong direction it flows from Lock Shield valve to TRV (Honeywell VT15) which claims to be OK either direction.
    4) Too much pressure, unlikely as build in by-pass valve in boiler plus second one next to boiler.
    5) Some thing else.
    I have been looking at the some thing else, and my thoughts are TRV head speed, it takes around 3 minutes for the valve to move from fully open to fully closed, when playing with the heads, I realised if removed when boiler is running within around 30 seconds the radiator is really hot, and it can take an hour or more to cool again, so if the valve opens fully even if just the exercise program during the day with really good insulation in the rooms, that room will raise in temperature and stay hot all day.

    There are three things which can affect the speed a radiator heats up, pump speed although since inside boiler I can't change that, lock shield valve settings, and water temperature, however all also have other effects as well, hence the post, I know with modulating thermostats like Wave the output water temperature is used to control room temperature, and I also know every time the boiler turns off, heat is lost out of the flue so ideal is for it to be cool before it turns off, and I know the Honeywell Y6630D thermostat is not really suitable as it increases cycling of the boiler, but I really don't want to run hard wiring, and cheaper wireless don't fail safe. So I know ideally I should swap the Worcester Bosch boiler to one which supports OpenTherm and swap all my TRV heads and wall thermostats to EvoHome, however that is not going to happen so want to know what changing the output water temperature does, will it increase or decrease cycling, will it increase or decrease efficiency, it is clear it will speed up or slow down speed at which the house can heat up, although not even sure on that, as if it results in a longer burn time, then it will also give the electronic TRV heads more time to get temperature correct.

    Seems the lock shield valves have worked to stop over heating of wife's bedroom, however still would like to know more about water temperature settings.
  6. The Teach

    The Teach Well-Known Member

    MGW is your boiler heating load (kw) matched to your radiators requirement ? if your radiators need ie 14kw and the boiler is temporarily pumping out 28kw into your radiators. The radiator will heat quicker the etrv will not react in time and show a temperature overshoot.

    Maybe just turn down the boiler thermostat and gradually turn it up as the weather gets colder :)

    which bosch boiler do you have ?
  7. Heat

    Heat Well-Known Member

    Really shouldn’t have a TRV on the hall radiator where it has the room stat.
    If the hall radiator is greatly oversized, then that creates a problem.
  8. Mike83

    Mike83 Well-Known Member

    Or undersized. The rad could get really hot shutting down the trv. The room then remains cool keeping the room stat calling for heat. The test of the house then overheats
  9. Mike83

    Mike83 Well-Known Member

    Room stat in hall with no trv is the tried and tested method.
    Heat likes this.
  10. MGW

    MGW Well-Known Member

    The use of a reference room to control the boiler means the boiler does not cycle on/off when demand is low or zero. The reference room must however have no alternative form of heating, and really needs to be on ground floor, so house has 5 down stairs areas heated by central heating. Kitchen with cooker, wet room with underfloor heating, living room with gas fire, best room with gas fire, and hall, so only option is use hall as reference room.

    As long as the front door is not opened one can throttle back the hall radiator with the lock shield valve so all other rooms are to required temperature before hall thermostat starts to switch off/on. But open that front door and hall gets cold very quickly, and then takes hours to reheat.

    So the compromise is a TRV on hall radiator and open the lock shield valve so it heats up quickly until nearly at target temperature, then slows down so rest of house can catch up if required. However the temperature of the two thermostats are linked together so two options, either have a set temperature for both thermostats, or link the thermostats, my intention was to link to Nest, however as yet not fitted Nest, and not sure if it will work? as at the moment around one degree difference between the two thermostats, the TRV turns off one degree before the wall thermostat. In real terms the TRV does not turn on/off and neither does the wall thermostat, the TRV gradually turns up and down and the wall thermostat uses a mark/space ratio to reduce or increase boiler output.

    The problem is turning off heating over night, I want a little extra time for rest of house to reheat before hall thermostat turns off heating, so hall TRV is set to 16 degs over night then 1/2 hour after central heating has switched on, it moves to 19 degs, this 1/2 hour seems to work well, and up to 10 am all seemed great, then slowly bedroom would over heat, however a combination of turning down bedroom lock shield valve and turning down boiler output temperature seems to have worked.

    Today all room temperatures were within one degree of target, so no more complaints from her in draws.
  11. candoabitofmoststuff

    candoabitofmoststuff Active Member

    I'm open to correction here, but my understanding of TRVs is that they are either open or shut...
    They may take a short while to actually change from open to shut, (or vice versa), but in theory they should operate partly open. They should be acting like an on/off switch.... "Right this room is at requested temperature, I'll turn off"

    Can you pros advise if my thinking is correct?


  12. sam spade

    sam spade Active Member

    No, your thinking is not correct.

    A TRV is a proportional control, adjusting the flow through the radiator so it is producing exactly the correct amount of heat. They are designed to be fully open if the room temperature is more than one degree below the set value and closed when it reaches one degree above setting. This gives a two degree band.

    TRVs can act like on/off switches, but this is normally a sign that the system has not been balanced correctly, resulting in excessive flow rates and high differential pressure across the valve.
  13. Heat

    Heat Well-Known Member

    That is correct.
    TRVs close off gradually - basically just a washer being slowly pushed down.
    Most of the time this means the radiator will be working at full heat whether the valve washer is open full up or nearly closed down.
    The thermostatic head sensor is really just a distance adjuster for the user.
    There will be a flow and output loss just close to when valve gets into a nearly closed position, but that shouldn’t last long.
  14. Heat

    Heat Well-Known Member

    A TRV does gradually alter the flow, but that does not always adjust the output of the radiator.
    They do actually work like an on/off switch.
    What people fail to realise is a radiator will be cold, or luke warm, or hot, due to the TRV being closed at a certain time, but NOT due to any thermostatic flow control.
    The only time when there is some real reduction in flow and heat output is when room comes close to TRV sensor set temperature and valve washer is close to off position.
    Yes, if you turn a TRV slightly from zero position until just a stream of water begins to enter radiator, then it will have a flow/temperature severe restriction, but that is not the function of the TRV and will not last long anyway.
  15. candoabitofmoststuff

    candoabitofmoststuff Active Member

    I've just realised that I didn't write what I meant...

    When I wrote;
    "but in theory they should operate partly open"
    I meant to write;
    "but in theory they should'nt operate partly open" (except during the phase where changing from on/off or off/on)

  16. MGW

    MGW Well-Known Member

    When fitting the TRV head the motor takes around 3 minutes to fully close the valve, then you hear it open again. During the day you hear the motor run for a few seconds as it adjusts the valve, it clearly does part open the valve, it is not a solinod it's a motor.

    Once one sets the temperature on your phone or tablet, it should reach that temperature, but not exceed it, however that has not been the case, what I have been trying to work out is why, is the valve base faulty, has it been mounted wrong way around or is it opening when boiler not running then can't close again quick enough?

    Or some thing else? Closing the lock shield valve does seem to have helped, so I wonder if as the pump starts there is too much pressure which is opening the valve due to supply being on the lock shield valve side, so closing the lock shield has stopped the rush of water opening the TRV.

    This is just a guess of course, but closing lock shield valve does seem to have cured the problem.
  17. Peter208

    Peter208 Active Member

    That's how we used to work it chippie. Worked like that for years but been retired now for a few and made some changes. Some of the changes driven by a change of life style and others by idle hands. Done some simple updating and heating control was one of them. Now when we see a "bit of a bargain" we pack and go and there's not much call for the fluffy dressing gown but the wife takes hers.
  18. Peter208

    Peter208 Active Member

    Are we saying that TRV can wear out? Is this common and should be expected or should they last for the life of the heating system. I've never heard that you should expect them to fail.
    MGW likes this.
  19. MGW

    MGW Well-Known Member

    I have clearly got it wrong, all diagrams I find show how pressure from radiator side of valve would tend to close valve not open it.

    This is the second time I have fitted them, also had problems first time around, fiddled and fiddled, then suddenly they seemed to behave them selves at the point where I gave up trying. Maybe some learning software in valve or hub may have finally worked out what to do?

    Attached Files:

  20. Peter208

    Peter208 Active Member

    I fitted cheap TRV a few years back, been as good as gold. Have made small adjustments as you do but all in all it was worth the time and little trouble to fit them. All are easy got at and 90% have a very good air flow around them ( don't really know if that helps ) My biggest improvement has been Hive. It has been very practical and reassuring during times away from home. We have gained so much more, above and beyond what was fitted without any disruption to the rest of the installation.
    MGW likes this.

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