Have three digital HW thermostats (two wires each, R &W) powered by batteries hooked up to Tekmar Zone Control 306V on 3 zones.
One day, just testing to see how it works, bought a Sensi WIFI thermostat and had it hooked up to include C wire connection by a separate 24vac transformer as in Photo# 3 and worked flawlessly. https://sensi.emerson.com/documents/sensi-wi-fi-thermostat-installation-guide-10-17-2-en-us-4278840.pdf
Then, since this Tekmar has an internal transformer, we decided to ditch the separate transformer and have it hooked up as in Photo#2. Operationally, everything works in terms of keeping the temperature fine and fires/stops the boiler fine. And we have heat. I can also use the Sensi cell phone app to do things (eg remote-adjust temp etc.).
But some features on the phone app disappear and Sensi Co. said “your Sensi only has ‘power stealing’ and you need to check with Tekmar”. And Tekmar does not have a support line. Just refer to the “Local Rep”.
I love to have this “Continuous Backlight” feature back for my old dad’s bad eyes. Any suggestion?