Tado app says heating? When heating is set below temperature

For ages I've had no problem with the Tado system.

But for the last few weeks this keeps happening:

I set the tado app to heat the house to - for example 19.5c

All good - house heats up, but then overheats to - for example 20.5c

The tado app registers the "Inside now" temp as 20.5c - correctly

Instead of turning the heating off Tado leaves it on!

Setting the temperature lower in Tado does nothing.

The only solutions seem to be to turn the boiler off and on again

I've tried force closing the app etc.

The app actually seems to be turning ON the boiler in order to be "Heating to" a lower temperature.

I can see the boiler receiving a request from the Tado thermostat for "More Heat" (Flashing rad icon)

I'm getting cooked here!

To confirm the usuals:

My iphone is up to date

My Tado app is up to date

The Tado Thermostat is connected to the wireless bridge and the boiler and has working batteries

The Tado Thermostat is reading the correct temperature.

The bridge is connected to my router, everything is connected to everything else

The boiler (Vaillant Ecotemp) is working fine.

The whole system used to work fine.

Just so you all know - on this forum - your question will be marked "Answered" as soon as anyone replies.

Even if the reply is just "I have the same problem with my Tado"

This can make it look like all the issues are solved immediately!

Solution:

Make sure you click "no" on "does this answer your question" button on any replies that do not actually answer your question.

You can always "like" these replies with a thumbs up to show that you appreciate the reply even if it does not solve the issue.

Of course it would be great to get email support from Tado themselves, but I imagine they are pretty busy!

This is not a criticism of Tado, or their forum, just advice from a fellow Tado user trying to get their heating to work.