UK (240v) room thermostat

Hardware
1

I’ve read this thread - and hope things may have improved over the last couple of years.

I have an old mechanical thermostat on my wall - it no-longer seems to operate reliably. I need to replace it.

I’ve not yet adopted Home Assistant - but I reject anything connected to “the cloud” - I’m exclusively interested in a local solution. The optimum product, for me, would be a device that is a slot-in replacement for my old mechanical room thermostat… that has a conventional thermostat functionality - but which can be remotely monitored/controlled (wirelessly) from home assistant. An imagined optimum device would have controls, which - if operated - override any commands received wirelessly… there would be a display… showing temperature, target temperature… and whether this was a manually set on this device, or set wirelessly.

Does such a device exist? (I know it would be possible to build one from scratch - but, really, I’d prefer an off-the-shelf device… if one exists.

Any advice?

The old thermostat is of this design.

2

Your thermostat seems to be 3-wire simple “switch”. You can replace it with some smart relay like Shelly (100% local). You could connect your old thermostat to smart relay (placed behind the thermostat) to switch on/off heating, but being over-drivable by home assistant or time schedule. Or use separate temp sensors to make automations on HA.

3

@Karosm That won’t work for me. I need to replace my existing thermostat independent of other concerns. I do want something which shows the target temperature (and ideally current temperature) and works (without home assistant) similarly to my broken thermostat.

Are you really telling me that no such off-the-shelf device is available - and making my own is my only option?

4

You are asking general HVAC questions. I’m going to be guessing at what will work as you haven’t given enough information yet. Any shop or technician will need the same information to be able to give you an honest answer instead of pushing you towards something that gives them the best profit margin for time expended.

What is the make and model of your old thermostat?
What is the make and model of what the wires are connected to? Is it a heat pump, airconditioner, underfloor cooling, hot water service, jet engine (yes, they have thermostats too), what?

Is the vendor of your existing equipment offering an upgrade path to make it ‘smart’? What?

What is the color of the wires connected, and to what port on the back of your old thermostat?

Is your old thermostat still working? Does it feel like it is mechanically worn out, or do you suspect the contacts are burnt out? Do you want to entirely replace it, or just enhance it behind the scenes, to make it smart? Is the equipment it is connected to working properly?

Any issues with WAF? Ask her! Will they be involved in reprogramming the new device to change the temperature too? Do they prefer doing it on the wall on on their phone with an app, or in HomeAssistant? Do you want to do this remotely away from home too?

How independent of vendor cloud control do you want to be?

How much do you want to get your hands dirty? Do you want to 3D print a new enclosure and make something from scratch using an ESP Relay module, or just wire in a new Nest or the suchlike? Is your time and futzing free?

I’m just guessing that you may just have a simple 24v pair that need to be shorted to turn on the other equipment when the temperature setting us reached. In which case pretty much anything will work - the HVAC industry has standards that have been around for many decades. Alternatively, you may need some proprietary reverse engineered protocol that is not industry standard to replicate. Until you give us more info, it is just that - a wild guess.

Once we have figured all that out, then we can make suggestions how to replicate and enhance functionality. Remember we are not in this for profit, so the advice you get here is probably biased by own experience.

5

The old thermostat is of this design.

No.

The old thermostat is a 3-wire mains-electricity affair (4 wire if we include earth). Wire colours shouldn’t be relevant - I think they’re red, black, yellow and yellow/green sheath over earth. It is wired as detailed in the link to it on Screwfix. It is connected to a gas combi boiler.

The existing thermostat is old and worn… it sort-of works, but does not reliably turn on/off at the set temperature. Sometimes the temperature falls 5 degrees below target before it switches on - or 5 degrees above target before switching off. It worked better several years ago.

While I am not a current user of Home Assistant, I’m confident with software. Right now, I want to buy a replacement for my existing thermostat. I would like one that works as a thermostat (and would work that way if home assistant was powered off or not present) but leaves open the options for home assistant to control it wirelessly in future.

I want to be 100% independent of cloud services. I want 100% of my heating system to be locally controlled. I do not want my heating system connected to the internet.

While I may be prepared to get my hands dirty in future, right now, I would like to buy a thermostat ‘off-the-shelf’ and install that. If that were the only Home Assistant device in my home - when I start to play with Home Assistant, that would be fine. I would be capable of building from scratch - but that would be an absolute last resort.

It is ~240 volt AC (UK mains electricity) - not 24 volt. The existing thermostat is, essentially, a mains ‘on/off’ switch (driven by temperature) with 3 wires (N0, N1 and Common).

I do appreciate that I am trying to scrounge advice from volunteers. I recognise that I’m being lazy… but I find it difficult to imagine that no-one else has dabbled with heating controls, for home assistant, and wanted to replace a thermostat with one that affords wireless remote control by some local protocol (independent of vendor cloud services).

I’ve looked online myself and have been very frustrated with the lack of clarity about how the products on offer actually work. It’s clear how the mechanical one needs to be wired in - the same clarity is elusive for digital and smart thermostats.

For example, I’m unclear about whether any of the many “wireless” devices could be (straightforwardly - without hacking software defined radio, for example) controlled by a local Home Assistant. The documentation for the “Drayton RTS1 1-Channel Wired Room Thermostat” is straightforward - but it can not be controlled remotely - and it is mechanical rather than digital. I would like a device like this (3-wire 240v AC) that is digital; can be wirelessly controlled (using some documented/open protocol - hence Home Assistant compatible) and - ideally - has a screen showing current temperature and target temperature info. I’m ‘moaning’ about it here because I’m finding the lack of clarity from the many vendors of devices that, at first glance, look suitable… rather frustrating. It would be great if a Home Assistant enthusiast could provide an anecdote of a device that ‘just works’… and does not connect the thermostat to vendor services over the internet. I’d hoped that there would be a curated list of products that work straightforwardly with Home Assistant… and that I’d be able to correlate that with pictures/prices.

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The simplest answer is there is no “local” thermostat that does not supply cloud in the same package from a reputable vendor.

There are plenty of 240V thermostats with a dry contact tough from aliexpress that just have wifi or zigbee

But if you want a brand name, honeywell t6 or netamo are perhaps a option

7

I have Hive and although it is primarily cloud based, it is possible to run them with ZigBee with Zigbee2MQTT,. without the cloud

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Thanks for the extra info. A photo of the front and back would be nice.
So basically anything that can switch on 240volts at about two amps when the temperature drops below setpoint will do the job.
Everything else is decorative.

Your gas combi boiler may have a diagram inside the door and specifications on a label that may also assist in device selection, having jumpers for different kinds of thermostat technology. Ultimately, that is the specifications you need to comply with. Sadly that information is not here (yet). The installers guide for most can prove to be most instructive.

Short term maintenance suggestion while you continue your investigations: Check your existing thermostat for cobwebs, spider egg nests, dust and fluff buildup, or other obstructions internally that may be interrupting airflow past the sensor (power off of course). Clean the contacts gently with a cotton bud dipped in hand sanitiser/alcohol won’t hurt either. Post a photo if you want comment on their condition.

Hysteresis is a normal expectation of heating and cooling, the mass of air and water taking time to heat and cool - not instantaneous. There are climate integrations that can account for this, switching on and off as the threshold is approached, some in hardware, and others in software. Common in HomeAssistant climate integrations too.

Consider a ESP32 board with a relay (usually rated 250volts at 10amps - more than adequate) and a display and some buttons and a fancy case and you could roll your own, or go with one of the vendor supplied ones that is cloud connected but can be customised to free it from the cloud by custom firmware from ESPHome or Tasmota or the suchlike. There are many designs, and even the ESPHome website at Thermostat Climate Controller - ESPHome - Smart Home Made Simple and Bang Bang Climate Controller - ESPHome - Smart Home Made Simple will give you some insight into issues to consider.

Where you place your temperature sensors (you can have more than one) is important. They are traditionally part of the temperature control case, but do not need to be. Keep them away from doorways and other places where they will give false readings. You can place your control and display in one place, the temperature sensors in another, and your relay portion near the gas combi boiler for maximum flexibility, convenience, and signal strength if you are going wireless (WiFi/ZigBee/Matter-Thread/BlueTooth, etc) or hardwired like RS485/ModBus, existing three wire mains rated cable etc.

You might want to call a HVAC installer to give you a free quote on an upgrade and pick their brains while they are at your home on what options to take. An old and experienced one will probably give you wise suggestions. Why stop at one - after a few you will get the common thread of what you need, rather than what is cheapest and nasty, or makes them the most profit.

The WAF factor is vital. Anything complicated and you sleep on the lounge tonight! Any knobs that invite random fiddling by passerby visitors and children are out. You shouldn’t need to have a padlock on the box over the controls, but consider child-proofing it by having to enter a code to enable any long term configuration changes. Even a separate BOOST button may be a viable option.

Everybody will jump in with their own suggestions on what to buy, but at the end of the day, your gas combi boiler is just waiting for 240volts to come down the wires to start it working, and when it disappears, to stop working - no more, no less. You can verify that by jumpering the control to live wires at the back of the thermostat and watch the boiler come on.

Feedback on what approach you take would be appreciated. Any further questions welcome.

9

I replaced the same old thermostat with a MOES WiFi Smart Thermostat

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I had to flash it with

Not sure if it’s as easy to do now but it was the first device for HA I flashed.
Flashed version doesn’t work of the cloud and can be used without HA. It’s so long ago I think I may have used the defunct tuya-convert over wifi(those were the days). Now you would have to attach to the pins and flash.

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Yes looks like it has to be done by serial connection now.

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It’s kind of strange, no-one sells simple esp-device with display (non touch), temp sensor, small relay and rotary knob for this purpose.

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LOL. Rotary knobs are so old fashioned. One of those haptic knobs would be great.

12

Why not just go with voice control?
Hey Jeeves, a little warmer please. Yes, sir, right away! Would you like toasty hot, or just a wee little more?

Alternatively, why not AI, where it KNOWS what you want and tells you so, emphatically, and usually wrong!!!

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Forum jammed…

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Still rotary it is. My point was: not some touchscreen adjustment that you need instruction manual and manicure to set the temperature

1 Like
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Be aware that any Tuya device flashing instructions may be dated, where Tuya will replace the controller board with whatever the flavour of the month is. What was a simple flash on a ESP8266 can now be a different processor board altogether and require a completely different approach to customise to your needs.

1 Like
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Sad but true. :disappointed:

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This is something I had feared. The retail sales pitch seems always to be “use your smartphone to set your thermostat when you’re not at home.” whereas I want a thermostat that has a well defined wireless interface for integration into a local network however I see fit. I would not object to a reputable vendor providing cloud services - but I’d want to know that my thermostat would not become dependent upon internet access (if, for example, the thermostat stops working if it doesn’t get an weekly/monthly/annual interaction with vendor services.)

The phrase ‘dry contact’ is new to me… I’m assuming a thermostat described this way would be equivalent to a mechanical 240v 3-wire thermostat if I connected N to one side of the ‘dry contact’ switch?

From AliExpress, I like the aesthetics of:

  • RS485 Modubs/Wifi Thermostat for Boiler 240V - however… I’m unclear if Modubs tells me enough about protocols… I feel uncertain whether connecting it to a local-only Wi-Fi network would work… I can’t find details about its accessibility over wifi… I presume it would DHCP - then either offer a web service or try to connect to one. If it tries to connect to one, it would be unfortunate if it were a proprietary one in the cloud… Reverse engineering that would be a pain.
  • AVATTO Tuya WiFi Smart Thermostat,Electric Heating/Water Heating/Water Gas Boiler,Work with Alexa Google Home - which looks at least superficially promising… however… I can find no information about protocols to interact over WiFi… and I’m certain I don’t want to use (or have the burden of reverse-engineering) the “Tuya app”. I’m not sure if I should be worried by “works with Alexa” - I’ve no objection to integration being possible - but do not want my thermostat integrated.

As I don’t want to provide smart devices with internet access, I’m guessing Zigbee variants would be best for me. I’ve never used this protocol before… should I expect good open-source support for any zigbee device - or is it more likely that I need more information to get to an API layer to interact with it? Should I expect Tuya devices to interact well with Home Assistant?

(More to follow…)

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You don’t need dry contact relay here.

To my opinion you shouldn’t have too much expectations with them…

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(Continued…)

I’m not sure I need a brand-name… but I am looking for something of decent build quality - that is of a quality I can depend upon.

Superficially the Honeywell T6 looks OK. I note that while it claims compatibility with “HomeKit” - it doesn’t claim Home Assistant support. My biggest concern with it is that its API might be provided via the cloud. I can imagine the device connecting to vendor services in the cloud - and the only way to interact with it wirelessly would involve dependence on cloud services. While price isn’t prohibitive - I note it’s about 6 times the price of the AliExpress Tuya ones… with which I have similar concerns about wireless access protocols.

I’m less enthusiastic about Netamo. I like the idea of making better control choices using temperatures from multiple sensors, including outside… but, if I were to use multiple sensors, I’d want them to be under Home Assistant control - rather than be proprietary tie-ins to a particular vendor.

(More to follow…)

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I would venture that two of the HVAC giants in the industry that have been around for half a century or more would be able to offer you anything you wish for, cloud connected, Tuya compatible, ModBus, dry contact or not. Honeywell and Westinghouse, both global players. Check both their websites and sales brochures. There range is vast, and covers everything the industry and customer wants dictate. They carry designs that haven’t dated in decades, doing their job faithfully, chugging along reliably. They also carry Matter/Thread devices, just on case you have to have the latest trendy thing to show off to your visitors, and brag about on Faceboob. Yes, you pay a little more for that reputation and reliability, but when you average it out over decades rather than months for Chinese devices, you do the math…

‘Dry contact’ is just relay output, isolated from other circuitry. Safest when cobbling bits from different vendors.

You are using terms in a manner that would indicate you are out of your depth. Call that local tradesman for advice - even if you pay him a few quid for his time and advice, you will save it long term if they honestly sit down with you and explain it all to you.

Another option is to tackle the local plumbing teacher from their trade school down at the pub and shout them a few pints.

Alternatively, a lot of hard research and steep learning curve ahead of you.