Veissmann S-Plan 2 pipe switch to X-Plan and OpenTherm
I've had TADO for several years and it works okay. My setup is a Veissmann Vitodens 100-W WB1B system boiler in a S-Plan 2-pipe setup (flow and return) with an Evocyl 259L hot water cylinder. I have TADO v3+ with an original extension kit with OpenTherm support running in 240v S-plan relay mode, and 10 TRVs dotted around the house.
This diagram shows my current setup with the extension kit jumper position set to 2 for 240v switched live relay mode to power the two NC zone valves:
So, I want to now switch to use OpenTherm as my boiler supports its and my original TADO extension kit supports it. That is the easy part, disconnect the 240v relay connectors to the zone valves in the extension kit and disconnect the boiler X1 relay. Then connect the two OpenTherm connectors in the TADO extension kit to the X21 connectors in the boiler. I have the the Tado Pro app and can easily reconfigure TADO to use OpenTherm mode.
After much research I understand it make sense to switch my S-Plan system to X-Plan/PDHW. This would mean changing the central heating 2-zone Normally Closed valve to a Normally Open valve. This is also not an issue in terms of plumbing and it all makes sense.
However the final part of this and where I am struggling to find an answer is how to control the zone valves in the new setup. The TADO manual clearly shows that the relays in the unit operate in dry contact mode and offer NC and NO operation which would correspond to the new C/H and H/W zone valves but because they are dry contact and the zone values are 240v this will not work.
How do I solve this problem? Can you get low-voltage triggered zone values that would work in this scenario? Or do you need some kind of additional "digital" relay to make it work?
Any advice would be greatly appreciated.
Comments
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Did you manage to get your system boiler working with Opentherm?
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Ok here is my latest plan… I'd love some feedback on my idea…
Three parts to the diagram below.
First the existing TADO, S-PLAN setup I have now working in RELAY MODE.
Second an interim phase where I switch over to PDHW using a Normally Open 2-port valve for my heating but keep RELAY MODE in place.
Third the final solution using OPENTHERM and DIYLESS OPENTHERM gateway to allow me to control a relay to switch the DHW circuit on.
ESP32/ESP8266 OpenTherm Gateway - DIYLESS Electronics
Comments please!
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In general, I like it. Viessmann, PDHW, X-Plan or 4 pipe, all good.
OpenTherm, Tado-flavour, not so convinced.
Can you not weather comp the Viessmann?
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Yes i could but im so invested in tado that i really wanted it make it work that way.
However that said, if i can bin Tado completely and use home assistant to do this I would do it. I know using the opentherm gateway is not far from this scenario but it’s not quite there yet.0 -
How do you see Tado ratifying the various calls for heat to set a demand % for OT?
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