LMSC
I had to replace a Y plan zone valve on my hot water this week as it was constantly demanding hot water from the boiler, but the boiler wasn’t asking for hot water.. Essentially the relay in the valve had died so the switch out (orange cable) had failed closed so was outputting 230v to the water request part of the circuit.
This made the boiler run 24/7 but with no water flow going out it was not using much gas.