What is OpenTRV

In the UK, the majority of us are heating our homes with hot water heated up by a boiler and circulated by a pump to radiators in each room of the house. It’s clear that it is not efficient to have a single thermostat to monitor the temperature in one room and use this to indicate to the boiler that it should start up and supply more hot water. It doesn’t take into account the rooms where no one happens to be at the moment – it’s not necessary to heat up a bedroom for most of a day if it is unused.

That’s the problem that OpenTRV solves. 60% of the domestic energy use in the UK is heating and 60% of us admit to heating rooms that are unoccupied. OpenTRV helps to get both of those figures down and saves you money through reduced heating bills.

How does it work? On the radiators, you screw on a thermostatic radiator valve (TRV) that can be switched on and off by radio. The OpenTRV control unit is a separate small box with just a couple of buttons and a single LED. It senses the temperature and whether anyone is in the room and if it decides or is instructed to heat up the room, signals the TRV on the radiator to open up. There is another OpenTRV unit attached to the boiler and when that unit hears the call from an OpenTRV unit to its radiator, switches on the boiler to provide hot water.

In essence, that’s it. There is a light sensor in the OpenTRV control unit so that rooms which are unoccupied/dark are not heated as much and a button to provide quick heat in case you feel that the radiator needs to come on immediately.

We like to think of it as a cosy warm bubble of heat that follows you around your home.


  1. John Stumbles

    Interesting project. I’m just doing a heating system for a geeky customer who wants Zwave TRVs driven by Razberry (for which he’ll write code). I’ll try to write something up as it goes along.

    I think it would also be interesting to hack Worcester-Bosch’s proprietary ebus(?) protocol in order to do weather-compensation without having to use W-B’s own expensive and inflexible FW100 controller, but that’s an exercise for the reader 😉

    Anyway I’m happy to help if I can. I’m a plumber & heating installer working in Reading and a few miles radius if that helps.

  2. Darren Miller

    Very interested to stumble across this. Towards the end of last winter I implemented my own system using Z-Wave TRVs, thermostats and a custom software “manager” to see if anything was calling for heat. The winter ended before I really proved it but I’ll be starting up again soon. I’d be interested to know how (or indeed if) you’ve found a way to overcome the following issues:

    * Build up of condensation in rooms that are unheated in cold weather. This can potentially cause problems that are more serious than a little wasted energy

    * Finding a sensible balance between battery life and wake-up times on the non-mains devices. I find this to be a key issue with Z-Wave

    * Modern “smart” thermostats contain algorithms to reduce gas burn as the property approaches target temperature. It makes a huge difference. Do your control units incorporate this and if so how is it managed with multiple and potentially conflicting requests? If they don’t incorporate it, do you have any data to demonstrate that there is a genuine energy saving compared to using a single “smart” thermostat?

    1. mark hill

      Hi Darren

      In answer to your question:

      1) Condensation: two things – one, don’t reduce the room temperature so much that the air can still hold enough moisture without it condensing out (not as efficient, but then again, neither it is a good thing that your soft furnishings/clothes get ruined); two, we are switching from just a temperature sensor to using a combined temperature and humidity sensor and so will be heating up rooms in which the humidity is creeping up.

      2) Battery life: We don’t have a problem with this at the moment – we’re pretty miserly with our energy budget and it works for us, at least for now.

      3) “Smart” thermostats: Some of these devices are using proprietary protocols that are inaccessible to us. That said, we are talking to boiler manufacturers as they are interested in the potential for two way communication with OpenTRV controllers. Also the OpenTherm Gateway looks ripe for integrating into a system with OpenTRV: see http://otgw.tclcode.com/index.html

      Compared to a single “smart” thermostat (monitoring the temperature in only one location in a building) zoning will typically be twice as effective (efficient), going by the claimed performance measures of the various devices available in the marketplace (we don’t have any of our own comparison data that you asked for as yet).

      If you want to ask any more questions, may I suggest that you pose them on our interest list http://lists.opentrv.org.uk/listinfo/opentrv-interest where you’ll get the collected wisdom of many subscribers, not just my two penn’ worth. There’s also a scheduled IRC on Thursday evenings.

      Regards, Mark

  3. Chris Nevill

    This sounds quite exciting. I was looking for something exactly like this a few years back. The closest I could find was Z-Wave but nothing really felt like a full solution and everything seemed to focus on the single roomstat. Is this all just theoretical at the moment or do these things exist?

  4. Paul Record

    Hi and interestint project. I have had control of my Central heating system for about 2 years using inside and outside temperutura measurement and time of day to determine boiler operation. The system is entirely wireless based on synapse-wireless modules which run and cut down version of python up loaded over the air. The inside temperature measurement can come from multiple locations based on hacked Lidl’s remote control sockets. The outside node is solar powered and the central heating controlling is mains powered. the next stage is to zone the house using TRVs – there are a few companys that sell motorised valves but they are not cheap.

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