Opentherm modulation with multiple zones/thermostats, UFH + Radiators

Kingwell

Hi There,

I'm currently planning a new combi boiler install with Tado thermostats, and the system will incorporate a wet underfloor heating system in one area of the house, and conventional radiator system covering the rest of the property.

I'm struggling to find information regarding how Tado thermostats can be used to modulate the boilers heat output when multiple zones are being controlled.

In my example, the UFH zone will be set up with a blending valve to regulate the water temperature being fed through the UFH loop, in turn this will be controlled by a Tado smart thermostat in an S-plan configuration using a two port valve to feed the UFH loop independently of the radiator loop.

Ideally i would like to be able to modulate the boilers output temperature as if there is no demand from the radiator zone, the boiler would not need to produce water any higher than ~40c to feed the UFH loop, likewise if the radiator loop is demanding heat, the blending valve in the UFH manifold will regulate the water down to the correct temperature for the UFH loop.

Is there any information available regarding if/how this setup can be achieved?

Can multiple thermostats be daisy chained onto the opentherm bus? Or can one thermostat act as the opentherm controller for the entire system and demand messages are passed between controllers?

Can the heat modulation settings be configured for UFH vs conventional radiator circuits?

If the extension kit were to be used as the interface to the boiler and zone valves, can the two outputs be set to heating zones instead of 1x heating & 1x hot water?

Any advice here would be greatly appreciated!

Thanks.

Kingwell

Yeah it's a little disappointing.

I went down the live chat route and discovered that there is no heat modulation support for under floor heating. Probably because the modulation is mapped around the temperatures used for radiator heating.

I also found out that the hot water relay on the extension kit cannot be used to control a second zone valve at the boiler for the purpose of heating. Quite a bit oversight as it means that multiple zones require hard wired thermostats. This is such an easy firmware adjustment too.

I wasn't provided with any info on multiple thermostats on the digital bus after asking. So i assume that this just hasn't been thought about.

I may have a play around with using an esp32 to control the heat output of the boiler as the implementation here would be quite simple acting as a man in the middle for the tado stats and the boiler.

It does just seem like the product lacks a little maturity at this stage, which would be fine if the information around it was more accessible.

princp

How did you get on?

I’m currently implementing something very similar: radiators controlled by tado smart thermostat/radiator thermostats/extension kit using OpenTherm with two wet UFH zones also controlled by separate tado smart thermostats.

From discussions with tado, Omnie (UFH supplier) and Viessman (system boiler) I’ve established the following:

• Wet UFH is controlled by tado’s mains on/off relays to the actuators AND wirelessly via the extension kit to the boiler but it’s not clear what water temperature will be demanded through OpenTherm
• Radiators are controlled wirelessly via the extension kit and the boiler will modulate following tado’s algorithms
• tado overrides the boiler water temperature setting (currently going up to 80C) but this can be modified by tado their end; I’ve asked for 55C which is the optimal temperature for the wet UFH
• tado cannot control valves to create distinct CH zones; I may do this via home automation. However, since the radiators all have tado thermostats, they can be off when only the wet UFH is needed. Just a shame hot water will be circulating in unlagged pipes beneath the floorboards.

I’m hoping that when both the radiator circuit and UFH are on, the boiler will provide water up to 55C. When the boiler provides water below this level (ie when it’s not cold outside and the wet temperature is close to the current temperature), is likely the UFH will heat its rooms slowly.

this should be setup next week I’ll provide and update on how we get on.

mpmcgoo

I would be really interested to know how your systems turned out?

I am just implementing something similar with UFH and radiators. I can see that a great system is almost within touching distance, but from the above comments and my conversations on live chat it might not be quite what I had hoped.

Unfortunately I have only just seen these comments, as I might not have wasted so much time.

It is difficult to find actual information how Tado functions. I am starting to learn a lot is done at a back-end, only accesable by the Tado technician.

AndyWebb1987

How did everyone get this working, or not as the case may be?

I am looking to set up pretty much this exact set up but using a Combi.

Any help would be hugely appreciated 🙏

Kingwell

Super delayed reply as i never got any notifications following the initial post.

Ultimately I used a tado bridge(driven by 8 radiator valves in the conventionally heated part of the house)+ additional thermostat (wired in the area served by UFH) to simply throw two zone values.
I then had an esp32 that was hooking the call for heat from the position switches in the zone valve (so the boiler didn't fire until the valve/s are fully open) and grabbing temperature data from the tado equipment via home assistant to drive the modulation on the boiler(36kw vaillant combi)

The end result does work well but the effort to get it working was far too high to bother doing it again given the inaccuracy of the radiator valves with the temp sensor far too close to the heat source.

Replacement for this is to use radiator/ufh zone actuators/home assistant/esp32 room stats which yields a substantially more robust result!