Wired thermostat as OpenTherm controller?
Bear with me on this one…
I have an S-plan system with a Viessmann boiler. The weather compensation on the boiler is basic (cannot fine tune the curve). It's ok, but not configurable enough to run it on it's own, with no internal control (e.g. room stat).
I've therefore been wondering (and this may well be a very long shot), is it possible to effectively replace the boiler WC sensor with a wired tado stat, connected to the boiler OT connections? (The boiler is OT compatible).
The idea would be to have that wired stat operating only as the OT controller, I think as the 'zone controller' to which other tado stat(s) - located where needed - would send temperature data.
Obviously, something (the wireless receiver) would still need to control the s-plan valves for CH and HW using relay, but then in place of WC, the wired-in stat next to the boiler would take the temp data from the other stat(s) and modulate the boiler accordingly, using OT.
Not sure if this is an unnecessarily complicated concept, but I think I recall once seeing a thread to this effect somewhere on here, but I can't for the life of me find it now.
Any thoughts much appreciated.
Answers
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Hello again.
Having explored this with Tado, it’s fair to say they don’t wish to mix OT or any other bus control with relay switching. I’ve seen Szymon of Urban Plumbers using Nest to do hot water priority and OpenTherm, so presume that works.
I’d have thought getting Tado to OT control your boiler, changing to X Plan and arranging a separate timer for DHW production would be simplest. I’m presuming your older Viessmann can be controlled or fudged to do the higher flow temps when HW is demanded. You’d be telling Tado to control it like an OT combi boiler.
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Thanks again @Montage. Yes, boiler has DHW priority fitted so goes full out when the HW calls. I'll have a think about X plan. Thanks for that. As you'll have gathered, exploring an option b to my other post (although I am surprisingly making at least a little progress with tado on that one…). Cheers again.
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The positive with X Plan is that it’s just a simple valve swap and it makes CH the default. So no switching of valves to do the heating and both valves move (one closes, one opens) to do the DHW. It would allow the decoupling you’d need to allow Tado to do OT.
Hope they get you sorted, either way.1
