Best device for status indication


I’m hoping for some advice on how I can give my instance of Home Assistant a signal to tell it the status of a device.

Here’s my Set up (Briefly). I’m running Home Assistant from a Raspberry Pi. I have numerous Sonoffs & Shelly’s all running Tasmota for lighting etc. I also have a Zigbee hub connected to the RPi for Temperature Sensors and Reed Switches. And finally, I am controlling the heating via a LC Electronics Relay board with an ESP01.

I am looking for a way for Home Assistant to monitor and display the status of a device without having necessarily changed the state before hand (if that makes sense).

One example of where this would be useful is in my heating system. I am currently running the ‘Smart system’ along with the old ‘Non-smart’ wireless thermostat system. I’ve tried to show how this is wired below (This would just be one zone, but for the benefit of the question, the purpose is the same).

Obviously, when the switch from the ‘old system’ is on, the boiler will initiate, but Home Assistant will not know due to the (smart) relay state remaining unchanged.
I was hoping to utilise the switched Live feed from the Zone valve as a signal to tell Home assistant that the boiler is on. But what would I use for this?

Any advice on hardware / config would be greatly appreciate.

If I’ve missed anything in terms of information please just let me know. I am definitely still learning, but am happy with what I’ve achieved so far. So am keen to learn more.

Many thanks in advance