we have a similar setup and replaced the thermostats with zwave devices on each room/heating loop. Keep meaning to make it properly smart, and e.g. switch off the heat when it’s a sunny day and we’re going to get lots of solar gain. But it works pretty well just as is.
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Hi Dan, this is pretty interesting - I’ve been considering what I think is the same setup as you, but I haven’t been able to get a definitive answer to the below. Can you help?
I have wet underfloor heating upstairs and down, with 2 manifolds, 2 wiring centres, and 12 thermostats. The thermostats are 230V 3-wire - Live, Neutral, and Switched Live - and I’d like to replace them with z-wave units in order to smarten my heating. My understanding is that each thermostat has a constant 230V, which is flips to the Switched Live whenever it has a demand for heat. The Switched Live then carries 230V back to the wiring centre and allows the wiring centre to handle the actuators. So, at it’s most simple, I could (theoretically - not that I’d actually do this - losing any temperature features) replace the thermostat with a bog-standard z-wave relay? What I’m getting at is: “can the Switched Live accept 230V without blowing up the wiring centre, or is the thermostat sending a down-rated signal or similar?”.
I’ve been looking at z-wave thermostats for UFH, but they’re all specified as for electrical UFH only, i.e. not water. Even the one you’ve linked says electrical-only, yet you use it for water. Do the electrical thermostats work in the same way as mine? I.e. the electricity is either on or off, binary, and not modulated to control the temperature?
My wiring is like this (no groups used; each thermostat has only a 3-wire to the wiring centre, and a floor probe): https://www.johnguest.com/speedfit/wp-content/uploads/sites/2/2014/11/JG-Wiring-Diagram-230V-Z2105-414-0817-WEB.pdf
Does your setup confirm that it really is as simple as I think but have been too afraid to act upon? In the UK at least, notwithstanding the contrary responses about continental wiring. Can I just replace my dumb thermostats with a z-wave thermostat designed for electrical UFH? I have my eye on these, but again they’re electrical-heating only: https://www.heltun.com/z-wave-heating-thermostat
Cheers,
Dan
Hi Dan,
How did you get on with updating your heating system? I have almost identical setup as you and need to make it (slightly) smarter. So far I have made a dummy set up with sonoff temp sensors and relays all working with MQTT and have been looking for options on here but some of the rules and waaay over my head.
If you have anything to share i’d really appreciate it.
Cheers
matt
Hi Matt,
I’m afraid I can’t be of much help - I haven’t made any modifications since my post above as I’ve no urgency and have had other projects to take care of. If and when I smarten the system I’ll post about it here, but for now I think I’m still too scared to break anything 
Cheers,
Dan
yeah probably not the best idea to fiddle with the heating with winter around the corner.
I realise I never replied to Daniel - apologies. But yes, my wiring is exactly the same - 3 wire 230V. Originally fitted with heatmiser wifi units which were terrible, and replaced with heatit zwave units which are flawed in a number of ways, but which do reliably permit zwave control.
I have a simple rule which, every half hour, compares the temperature reported by each thermostat with the target temperature (adjusting the reported temperature to deal with the unreliable heatit sensors). Then if 0.5C above the target, it sets the thermostat temperature to 10C (i.e. turning it off), and if 0.5% below the target it sets the thermostat temperature to 30C (i.e. turning it on). This keeps the place nicely warm - fairly large, with seven underfloor heating zones.
I keep meaning to make this smarter, e.g. avoiding overshoots, and cutting back when solar gain is anticipated. But I haven’t gotten round to it, and it works sufficiently well that I’m not very motivated…
Dan
No indeed, but at times you have to.
I just ran into a cold bathroom because my zwave actuator to control this heating zone dropped off the controller, something I still don’t understand how that can happen without manual intervention.
Just to remind you that you/we are creating a fairly complex system which is more likely to fail than the “dumb” systems you’re replacing. Also remind you OH server availability is crucial.
My code evolved over time, too, now mitigating overshoots, too, and validating sensor input. That latter you should put substantial work into.
I’ve also been thinking how to incorporate solar gains but haven’t gotten round to it. Still looking for the best algorithm to anticipate these and how to incorporate that in my control loop.
And I’m just worrying how to keep the system stable (and the house warm and my wife happy) while working on it.
I find there’s enough thermal mass in the house that the heating would have to be off for hours before anyone noticed. And I use the expire binding to notify me if any of the thermostats fall offline.
That’ll catch some issues but I feel it’s always something new to happen that you haven’t thought of before it happened to you once. And remember you also have to “debug” the classical part because no HVAC guy will want to take responsibility.
I once had my classic system fail because the outside temp sensor broke. A simple resistor, that was. The controller misinterpreted the measured value as the range minimum (-39° C, that was) and kept firing the boiler over and over. We didn’t notice for quite some days because it was summertime and already hot. So it was a HW failure plus an ever-in SW bug (btw a resistor they charged 80€ for, yuck!) .
I have a love-hate relationship to HVAC stuff since.
Well my system is completely reliable with multiple fail-safes. Except that the SSD just failed and right now the whole thing is down.