Heating controls n00b questions


I am very new to home automation and have some really dumb questions regarding heating (I am an IT guy, I don't understand much about the workings of heating!)

My (UK) house has a boiler that drives radiators and currently has a 7 day programmable thermostat (nothing clever here its not a smart device)

In my mind, I want to swap that thermostat for a smart switch (to fire the boiler) and then add smart TRV's to all of my radiators.

What I can't get straight in my head is the logic for how you set the the boiler to fire?

If I want my lounge to be 21 and my bedroom to be 17, is the boiler firing constantly if ANY of the TRV's still haven't achieved the desired temperature?

My concern is that I'll go from a fairly easily understood pattern of energy usage to one where the thing is blazing away all day to try and achieve an unachievable temperature goal somewhere in the house.

A few months ago I'd have been happy to mess around, but these days I need to be thinking about reducing costs with smart technology not wasting money.

Can you help this n00b please?


Think of it this way, I suggest: The job of a TRV is to determine whether the temperature in a room is sufficient (or not). If so, it closes (or stays closed). If not, it opens. That's really all it does, and it's depending on the fluid (water or water mixed with glycol) being supplied to it to be hot, so that heat can be exchanged via the radiator.

But you still have the problem of needing that fluid to be hot. If the boiler doesn't come on, then the fluid won't be hot, and so there will be no heat to exchange. In a system with a central thermostat, that thermostat is telling the control board on the boiler to turn on, so that the fluid gets hot. If you can have each TRV serve the boiler control function of the central thermostat in addition to performing its job of just opening/closing based on the temperature of the room, then what you have done is simply distribute that function of boiler control around the building, instead of having it reside in a single device. And the boiler will, out of necessity, need to come on when that TRV requires heated fluid. So, yes, the boiler may theoretically run more IF you desire the temperature of some rooms to be warmer than the average temperature of the building would have been using a central thermostat. And if you don't have the system built so that the TRVs can tell the boiler to turn on somehow, then you'll need to have a central thermostat set so that it turns on the boiler when any of the TRVs might need heat (i.e., it would need to have a higher setpoint than any TRV).

What TRVs do is create zone heating, and the theory behind zone heating is that your boiler won't need to run as long as would be necessary if you wanted the entire building to be the same temperature as the highest temperature room. Overall, it's generally a good idea. But the boiler is going to need to turn on whenever any TRV needs heated fluid, period. Otherwise, you have no heat to exchange through the radiator the TRV controls.


I'm no expert, but here are my thoughts:
-Is Hubitat really up to controlling mission critical stuff like heating?
-Doesn't your heating system have to be plumbed so that TRV's for individual radiators can work?
-How modern is your boiler? They modulate pretty well nowadays, I think especially with gas.
-I have an old cast iron oil boiler, but a large buffer tank (that I got with my pellet boiler) that I like.
-I think the more a boiler is on the better-hence the modulation



Is heating mission critical? Don't people use it for controlling heating? Nest is really popular in the UK (I don't know where you are?) so "smart" heating is definitely a thing.

To use TRV's you just need to make sure you don't put them on every radiator or have a bypass built into your plumbing (or so it appears from doing a lot of google)

Modulating boilers aren't a thing in the UK I believe.... in Europe yes, but not here. UK boiler thermostats are still on-off.

Thanks Madcodger - I think that makes sense.

" if you don't have the system built so that the TRVs can tell the boiler to turn on somehow, then you'll need to have a central thermostat set so that it turns on the boiler when any of the TRVs might need heat (i.e., it would need to have a higher setpoint than any TRV)."

Yes, I thought that I'd use a smart relay to control the on-off, using logic based on time (ie its evening, lets turn the heating on - like my 7 day programmer) AND if one or more TRV's were reading not at set temp.

That was my thoughts so far.... I'm sure I've not thought it through well enough yet.

Just a consideration, but Nest and other smart thermostats are, even if all their smarts fail for one or more reasons, still dumb thermostats with wires connected directly to a boiler or furnace to call for or shut off the heat when the room temp goes below or above the thermostat's internal setpoint.

Adding a home automation hub like Hubitat in the middle, depending on how much one decides to use it (and the sensors and actuators connected to it, many of them wirelessly) to take over the built-in functions of a smart thermostat connected directly to the heating source, does have the potential for serious consequences if one or more parts of the whole system (including any of those sensors and actuators) fails.


I hear you @marktheknife

One of the things I've been keen to try and not purposely do with my HE is to create something that needs my technical skill to control if anything goes wrong. I want things with manual controls as well as automation capability. (I started with lights a few weeks ago to learn how the thing works but keeping it all with a manual override!)

I thought I might replace my programmer and receiver with this:

Which as you say, if all goes totally wrong it would enable a manual turning up and down of a single thermostat and turning on and off of the firing of the boiler...

Using the receiver part of it as my relay.

I'm surprised to find there aren't many choices in the UK for that sort of product - I'd have thought all of the usual suspects (drayton, Honeywell etc) would have created something similar but it seems that everyone seems to want their "smart" stuff connected to their own app via their own cloud.

I know only too well in IT that cloud means "until they decide to turn it off" so am banking on HE to be the solution to that fear.

Your concern is well-founded. Inserting a cloud server into the mix for something as potentially catastrophic as home heating control (if something goes wrong and depending on where one lives) is a notion that should be dismissed outright, IMO.

A hub like Hubitat, with totally local access and control of devices, removes one of the most concerning failure points over which each of us has little control, an active internet connection and a functioning remote server owned by someone else.

My personal preference is to use a relatively "dumb" smart thermostat, similar to the one you linked to. We have several options available in the US, I have one that is wired to my boiler and pairs to hubitat with Zigbee. I also have a WiFi TRV that can communicate locally with Hubitat made by Shelly. I believe they're based in the UK, so you might want to look into what else they offer in the category of heating controls.

My use case for TRVs is a little different though. My master bedroom usually gets too hot when the boiler cycles on. So the single Zigbee thermostat wired to the boiler is used as the house's setpoint, but the TRV can close off individual radiators when the room is too hot.

That doesn't do anything for our guest bedroom on the top floor of the house that can get too cold, unfortunately. But I also have a mini-split AC in that room that can be used for supplemental heat in there if needed.

This solution with a TRV isn't perfect, but it also avoids anything truly dangerous throughout the whole house if the hub or TRV were to stop functioning as intended.

I have purchased the Zigbee TRV controllers below and intend to use them with my main programmable thermostat in my flat (UK) with "Tuya Wall Thermostat" driver by @kkossev
Note: the thermostat controls a Heat Interface Unit (HIU); communcal boiler is located in the boiler/plant room.

Ali Express - Zigbee TRV's

Moes Trv Zigbee 3.0 Tuya New Radiator Actuator Valve Smart Programmable Thermostat Temperature Heater Alexa Voice Control - Temperature Sensor - AliExpress

I do not want to purchase a new programmable thermostat with WiFi or Zigbee capability; this thermostat has a boost mode which gives 1 hour heating time and I intend to use a Switchbot to "push" the boost button! :joy:

Main thermostat

TRV in each room/hallway:

Zigbee TRV's

I will then write a rule to turn on the main thermostat when heat is required by any of the individual TRV's.

I did my smart heating before I got Hubitat. I just got the Honeywell EvoHome kit which consists of a touchscreen controller, motorised TRVs with LCD display and a boiler relay (straight swap for room thermostat without altering wiring. Everything can be controlled by the app and it creates a multiple zone system. The TRVs are a lot smarter than other valves as they learn how long the particular room takes to heat from any given temperature. With optimisation On, the valve will open at a time before your set point so that it is at the correct temperature, rather than guessing and altering the set point to suit.

There's a community app (unmaintained) and I have mine in Hubitat, controlling some aspects from rules (switch off when door open x minutes, cancel override when bedtime routine started etc). I've had mine about 5 years now and have had no issues. Search 'evohome shop' - they do various starter kits.

This is exactly my intention. I have UFH downstairs on my house with each room controlled separately. I intend to use the Moe's House TRV's upstairs which will override my upstairs Room Stat with a Rule Machine rule. I.e. if any TRV calls for heat, then make room stat call for heat. If all TRV's are satisfied, then make room stat satisfied. PS I'm in the UK and use Heatmiser Room stats with HE and they're seamless :+1:

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Many years ago we remodeled a small ranch style home that had baseboard hot water heat. I plumbed in a manual thermostat valve made in Germany as I recall) and a bypass pipe into each room. The boiler was controlled by a thermostat in the hallway. That system was probably the most comfortable I've ever experienced, as long as one could live with the hallway always being the warmest place in the home (that was fine as it was just off the living room). The really nice thing was being able to cut back the temperature in the bedroom without affecting the rest of the home. I mention this to point out that we don't necessarily need to automate everything, in terms of making it electronically connected to a controller. As far as I know, that system is still chugging along merrily, well over twenty years after it was installed. There's a beauty in simplicity that we sometimes forget.

My 2 story house has 2 zones: one upstairs and one downstairs. No bypasses, just 2 loops. It would be nice to control each room individually, although downstairs is open.

I think my pellet boiler modulates down to 30%.

It's a little hard to modulate my wood stove, but I try. :slight_smile:

I use this method. It's ace.


Although if I were starting a new build (or a major redecoration with rewiring), I would absolutely go with your wired actuator approach; I don't like the extra visible wiring that entails though, so I'm using some wireless TRVs. I tried a couple of Zigbee versions from Vesernet, but both had terrible battery life (like < 2 months), so I've switched to the Shelly WiFi TRVs which seem to be doing the right thing so far. A trial purchase of 4 still shows 100% batter life after a couepl of weeks - let's see.......
My issue though is finding an integrated device to control heating and DHW - I currently have a 'Drayton' controller that uses a couple of relays to do that - all the boiler controllers I can find (if I'm reading the the information correctly) have a single relay output to demand heating, and not a second one for DHW production.
I could of course home brew something (I've used a Fibaro smart implant to great effect elsewhere), but something integrated (including the PSU for example) really appeals.
Any pointers?

I'm not sure. I can tell you that my boiler initially had a standard thermostat attached, which has a single dry contact connection to the boiler.

Water is on demand regardless.

Heating kicks in on response to the thermostat. Or, now, in response to the relay.

Is that perhaps a combi boiler?

I have a 'megaflow' type HW storage tank which needs to be heated ahead of time - I've already switched to heating that electrically at night using the immersion heater which is now cheaper (on a low night rate) than using gas - but that's not necessarily always going to be the case, so I'm trying to cover all my bases.

Ah :wink: yes, combi here.

A little update as I like to share my experiences in case they help someone else...

In the end:

I had my radiators rebalanced by someone who knows what they are doing. Made a big difference to the effectiveness of my heating!

I deployed zigbee temperature sensors around the house and logged their output to influxdb and graphed it using grafana. This gave me visibility to tweak the (manual) TRV's.

Finally yesterday I installed one of these:

Absolute b***h to get working with HE - really struggled with that despite having read dozens of HE or ST pages about it. The device has a load of cryptic menus that aren't documented in the book that came with it - several of which are critical to making the damned thing work with a hub.

Working now :slight_smile:

Running the Thermostat scheduler and its working!

Only one downside with the thermostat is that because its a battery zwave device its frequency of waking up is quite slow. Doesn't really matter with heating scheduling I guess, but it can take up to 600 seconds to catch the commands.

Anyway, this and other things I've got working with HE are really good. Its largely down to the wonderful people on this forum... thank you all!

PS next step, now I have it under electronic control, work on clever things like leaving or approaching home :slight_smile:


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