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In a way I know the answer, wall thermostat turns heating off when we have warm weather, but I look at the PC and it shows me the target and current in each room from the electronic TRV heads, and I thing if it can tell me when room is cold why can't it be connected to boiler and switch it on when required. Why do I need a Nest Gen 3 wall thermostat which does not seem to connect to any of the Energenie TRV's even though the Nest mini can read out all target and current temperatures?

This house not a modulating boiler, but even when I had one, it did not switch off when all TRV closed then switch back on once one had opened. It seems it monitors return water temperature, why no return water flow?

If all TRV heads are closed, and the by-pass valve is in the boiler, if boiler starts pump and by-pass opens then boiler must know it does not need to fire up, OK wall thermostat to stop pump running is summer maybe, but running the pump stops it sticking, so not a bad thing to run it, as long as some anti-cycle software to stop it running too often.

So with all TRV heads on every radiator why do we need a wall thermostat?


The way I understand it is, If you think about the way TRV’s are used; in your living room you might have one that is not quite fully open, and one in your bedroom that is only just turned on. I say on & off, but they are more like blending valves.
So if your living reached temperature, there’d be no requirement for heat from the boiler, but the bedroom might need some. So the boiler will be cycling. A room stat with TRV's will 'complement' each other. If the wall stat is fitted in the likely used coldest room (i.e. not an unoccupied bedroom), then when that has reached temperature, the other rooms (with TRV's) would probably not need heat.

Some boilers I believe, are fitted with a flow meter valve, to sense when no TRV's are open (i.e. no wall stat); otherwise just sending heated water through the by pass is just a waste of energy.

You should consult your boilers manufactures instructions, on the method of controls. Its not just about heating your rooms, but about maintaining the efficiency and safety of your boiler.
I have had this conversation with so many gas engineers and their answer is that it is no longer referred to a Thermostat its a safety interlock incase the return stat in the boiler fails it can shut down the boiler ????? -------- if you ask me but that is what they need/install to meet their regs?
Just like the bonding issue their regs say that the bonding wire needs to be within 300mm of the isolation valve and our regs state "correct me if im wrong" 300mm from the isolation valve or at the point of entry into the building before any Tee's !
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I have the wall thermostat in the hall, not really the best room, but the wires were already there, so it was the obvious selection as only needed to connect up, did not need to run new wires, the bathroom has no TRV and is thermo-syphon with the domestic hot water heating, and the toilet has a liquid filled TRV.

The rest of the rooms have electronic TRV heads and each room has its own independent program as to when room is heated.

The idea was the dinning room, hall and living room would use a follow command and would auto follow what the wall thermostat does, however this did not work, if I altered the wall thermostat setting with my phone, the TRV heads would follow, but if I set a schedule for wall thermostat or turned the dial it would not follow.

The wall thermostat is on entrance level around centre of the house, so for a single thermostat around the best place to sense whole house heat, however there is a staircase opposite to hall radiator and two doors between hall radiator and wall thermostat which results in a delay in heat reaching wall thermostat.

To counter the delay in the morning the last 2 degrees are done 0.5 degrees per hour, this keeps boiler cycling at least until mid day, so all rooms in the house can heat to there set schedule, it drops 0.5 degrees an hour before we want dinning room then up again 0.5 degrees as dinning room temperature increases to ensure boiler runs.

I am sure if all rooms were kept at steady heat 24/7 the system would work A1, but the whole point of programmable TRV heads is the rooms are not kept at a steady heat 24/7, I have noted the hall radiator is normally around 2 degrees colder than the wall thermostat in the hall, so TRV head matches this, so in a day when we are all home it works reasonable well.

However the hall wall thermostat has geofencing and occupancy detection, another good reason to be in the hall, so when we go out, the heating auto reduces, and when we return it auto increases again, if I remember and turn down heating 0.5 degrees on return an hour latter I can turn it up again giving other rooms chance to catch up, I could set the TRV heads to geofence, however they clearly can't heat the house if boiler switched off, and being open a little more on return does mean radiators get hot fast for the recovery, so does not really need the TRV heads set to geofence.

The system of a way works, but I am sure if there was a sensor on the pump to switch off boiler and pump when it detected the TRV heads had restricted the water flow it could work much better, maybe not in this house as pump on the return, but sure it could work with many houses, again this house boiler cycles it does not modulate, but with a modulating boiler can't see why whole control should not be by the water pressure and temperature, it would make installation so easy, fit boiler, fit TRV with programmable heads, and all rooms independently controlled without the need for complex wifi links and thermostat/hub like with the EvoHome which seems to be the best system to date to control individual rooms. OK Hive TRV's do send a demand for heat, so seem reasonable, but the TRV heads are so expensive, upstairs my programmable heads cost £15 each, and so easy to use a room, no getting out phone, simple walk to radiator press button and it goes from Eco to Comfort until pressed again or programmed change, OK can alter with phone bluetooth, but no need, if I walk into bedroom early I just press button on the TRV head.
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@Dabbers what we don't want is high current through a gas pipe, so bonding needs to be after the point where it is isolated from earthing into the ground, so if some one steals copper and the TN-C-S earth is lost, the imbalance does not go through the gas pipe, or it could melt the gas pipe and ignite the gas. Which as I am sure you know has happened.

The point where gas is bonded needs come common sense.
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I've always gone to the isolation valve and yes I agree wholly with your comment about bonding, my point and biggest gripe is that the gas regs and the electrical regs are not the same. and probably never will be !
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My point with post, is it seems the modern central heating is in the main a hotchpotch of independent ideas, huddled together with no real control until you move to the super expensive wifi enabled TRV heads, and then we have a whole selection of devices that will not talk to each other.

OpenTherm was a step in the right direction, but you can't have two OpenTherm units working the same boiler as far as I know?

Back in around 1985 I came across the first modulating boilers, they had to modulate to keep cool enough for the latent heat to be used, the condensating boiler. And the idea was the TRV controlled the whole house.

However there is a number of problems with the early TRV with wax or liquid heads, they were not programmable, and showed *123456 rather than a degs C or even F which people understand, as the TRV closes it opens the by-pass valve so return water gets warmer, and once the boiler can't turn down any more, it starts cycling, every time it turns off, assuming pump also stops, any heat in the boiler is lost up the flue, the OpenTherm tries to redress this problem by ensuring before the boiler stops the water is reasonably cool, but cleaver algorithms can do this anyway, and also some anti-cycling software can reduce how often the boiler fires up to test if required.

However there is really no need for the boiler to fire up when the TRV's are still closed, if pumping water still lifts the by-pass valve, then not enough TRV heads have opened the TRV enough to be worth firing the boiler.

However the main problem is as the user, we really don't know what is going on. When a modulating boiler turns off, does it restart at same output as it stopped, or does it return to maximum output? This is an important question, as if the wall thermostat uses a mark/space ratio to stop over shoot, it could as a result increase waste as boiler is forced into maximum output mode, and loads of energy is escaping out of the flue.

If I could look as a gas boiler and it says output 20% or 80% then I could work out what is going on, but can't clip on an ammeter over the gas pipe to see what is going on.

OK the gas man may be able to read the input, but the guys I had call at this house to service the boiler and alter pipe work, looked at my set up and admitted they had not go a clue how to set it up. I could hardly believe my ears when the oil boiler expert say how he fitted a motorised valve without plumbing in to use it as a delayed switching relay.

There must be a better way to control out central heating, and it is normally down to the electrician to work it out, not the plumber, but we want it in a way which is in some way a standard, be it C Plan, Y Plan, W Plan, S, Plan or an electricians plan shall we call it an E Plan that can turn a reasonable system into a good system.

So I look at what we can measure, and what we can control, in the main a radiator (rather poor name as most of the heat is with convection) will produce a thermal circulation of the air, just like the DHW has a thermal syphon of the water, so under the radiator we have the return air, this is likely the best place to measure the temperature of whole room, a little up and to the side where most TRV heads are mounted is not far off the ideal place, and the Energenie TRV head I use on 4 radiators has two sensors one water and one air the former compensating the latter, and I can confirm placing a thermometer in centre of the room the recorded temperature is very close to the current temperature shown on the PC from the TRV head +/- 1 deg C.

So the TRV seems a good start with control, the wall thermostat is often not placed when it can read an average room temperature, in old house it was on the wall between garage and house, and the cold wall resulted in it reading rather lower than actually room, this house it is central, but too far away from radiator to be within natural thermals.

So other than using really expensive EvoHome or Tado how can we design a reasonable system? It clearly has to revolve around a TRV head, but not a super expensive TRV head, the Terrier i30 and the eQ-3 which I use are half the price or less than the wifi heads, so basing a system around those heads seems to be the way forward.

The TRV head can stop a room over heating, but can't fire up the boiler with the cheaper versions, so looking at a way to allow the cheaper versions of the electronic TRV to fire up the boiler when required.

So the area I am looking as is coolant flow rate.

All comments welcome, even if you say I am daft, looking for how you would enhance control on a budget?


Advent Win
To be honest I'm happy with how my system works, and it's a pretty standard one. Recent Worcester boiler with room-stat/wi-fi linked controller unit. Standard TRVs (not wi-fi, shock horror!) on the room and bedroom rads.

Reasonable bills and no over-complication. With the way I have set the programmer up we get the house/rooms at the temperature we want. Seems like a winner to me.
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First house hot air heating, it worked, expensive to run, but 1970's no double glazing.

Next house, bedrooms got too hot, and living room too cold, added extra radiator to living room (open plan) and standard TRV's up stairs, wanted room where cistern was so had main 7 water heater this was before the combi came out, and from that point single thermostat worked fine, however did have a Myson fan assisted radiator so air was circulated.

Then returned to mothers house to look after her, what a nightmare, trying to get heating right tried all sorts, problem was bay windows, so sun out and room at 28 degs as radiators take time to cool, but sun in and 19 degs C. Doors on every room did not help, and also well insulated so once hot, stayed hot.
In the end fitting a TRV to hall radiator was biggest improvement, so much for not fitting a TRV in same room as wall thermostat, only after fitting it did the heating work reasonable. But also using programmable TRV in living room means it acted faster and still would over shoot when sun came out but only to 24 deg C.

This house moved from gas to oil, and it was in a state, to turn on heating had to walk outside to converted garage and plug in the pump, there were three FCU plus a socket feeding different parts, and you could not turn the heating off half of the time, no motorised valves, two zones with two pumps one for each zone, but when one zone ran, it would force water in reverse direction in the other, so had two zone valves fitted to stop back flow, also put it all on one FCU and used a Nest thermostat as two wires take all coms thermostat to heat link and charge battery. One wire of three core and earth was open circuit so that was how I got DHW and CH control with just two wires.

However oil is not that reliable, regular have to go down and press reset button, and boiler does not modulate, so although do get a mark/space control, no where near as good at gas, we get quite a large hysteresis which is mainly due to single thermostat for whole zone of 11 radiators, not used second zone with 4 radiators.

Be it mark/space or modulating boiler one should be able to work out when the heating is satisfied or not by feed and return pipe temperatures, or some heat store, latter would allow mark/space boiler to work like a modulating boiler.

But step one is collect ideas on how to control, then consider if it will work here, and using the TRV heads without using the wall thermostat would be likely far better, but can't be the first to think this, so why is it not already done? I have missed some thing, so what have I missed.


@EricMark I take it when you say you have to press the reset at the oil boiler you mean the high limit stat? Having to do this regularly would indicate that there is a problem, normally this is the pump but it could be the stat at the boiler isn't cutting out.

Oil is very common over here, there are no issues with the oil boilers being reliable.
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@EricMark I take it when you say you have to press the reset at the oil boiler you mean the high limit stat? Having to do this regularly would indicate that there is a problem, normally this is the pump but it could be the stat at the boiler isn't cutting out.

Oil is very common over here, there are no issues with the oil boilers being reliable.
Flame failure relay is what trips. Been like that ever since I moved in, did get it services and jets changed and photo sensor but still fails to light around once a week.

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