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.
