Right now I’m involved in single combat with my boiler. It doesn’t talk to my thermostats or perhaps the other way around. Fortunately, If I jumper two wires together it runs until I pull the jumper off. Heat in the evening, unplug, then get up at 3Am and start again until 10 AM.
Sounds like the heater we had when I was a kid................
Sounds like there is a broken or corroded wire between the boiler and the thermostat. Since the jumper works, the boiler is ok, and at least part of the wiring is ok.
Perhaps a relay at the boiler end has bad contacts?.................