Tado X failure to communicate with central heating

After a LOT of trial and error, and installation of a bypass system by the service company, I finally managed to get Tado X working as expected in February of this year. I turned off the heating in March or April, and when I wanted to turn it on again, the central heating doesn't respond.

I have a wired Tado X Thermostat, connected to the boiler using OpenTherm.

What I've managed to verify so far:

* I've started up the boiler manually and it will heat perfectly, so mechanically the heater works. * The OpenTherm connectivity with the Tado app also works: I can change the hot water temperature in the app and the boiler hot water temperature is immediately adjusted. That means the wired connection to the boiler also works. * However, when it comes to heating, the boiler does not respond, even when I turn on heat boost mode.

I suspect a recent firmware update has broken my setup. But I can't find any information about that, so it's pure speculation. Nothing else changed in my home setup.

I've been in touch with Tado X support, and have raised it as an emergency, but they have been slow to respond and don't answer to in-depth questions. They made a change to set the vendorID on the Thermostat. BTW: It's borderline insane that I don't have access to those settings as an owner of the system! Effectively I depend on Tado to change every configuration option...

In desperation I've now tried to reset the Tado X Smart Thermostat. Unfortunately the app is also unable to add the Smart X Thermostat to the Tado app again: it gets stuck on "Searching for device" and then returns the error "Your Smart Thermostat couldn't connect.".

Has anyone had the problem I am having? I'm curious what you can share.

My boiler is a ATAG A244EC HP.