Boiler doesn't fire after simultaneous demand for heating and hot water
Let me explain the setup I have and what's happening.
We have a Vaillant EcoTec boiler and a hot water cylinder. There's a Honeywell controller with a valve that controls whether the hot water from the boiler is running through the rads, the cylinder or both.
So, all our hot water is pre-heated and stored in the cylinder.
When the boiler fires a radiator symbol on the display is shown (which is when heat is being called for I guess).
Our heating runs on a schedule which just varies the temperature a bit (lower overnight, higher during the day). The hot water is set on a fixed schedule in the early morning for an hour or two and again in the evening.
The problem we have and this has been an issue pretty much since the original Tado was installed is as follows.
If Tado is calling for heating and hot water at the same time, once the scheduled block for the hot water finishes, the boiler no longer fires for "just" the heating. It remains off. To get the heating to come back on again I have to hard power cycle the Tado boiler unit (which also resets the boiler and Honeywell controller as well). When I do this, after a couple of seconds I hear the relay in the boiler extension unit "click", the radiator symbol appears on the boiler and it fires up. Power cycling the boiler by itself makes no difference which suggests something in the Tado or the controller or perhaps the wiring between the two?
At this time of the year when the boiler is running most of the time this is now becoming a royal pain. Any suggestions on how to trouble shoot this and who could diagnose it for me?