I need to replace a failed thermostat in my living room. I have a simple electric boiler supplying hot water to underfloor heating - this is switched by an OJ Electronics WLM Master Underfloor Heating Controller (now discontinued). As well as the boiler, this controller also switches the pumps and opens the actuators on the UFH manifold and has a 2-wire low-voltage bus to which 4 seperate zone (room) thermostats are connected. The thermostats are basic OJ Electronics WLTA-19 dial adjusted thermostats (not mechanical), also now discontinued. One is no longer working and I need to replace it. There are 2 thin wires running from the thermostat to the low voltage bus (+ to + and - to -), they obviously don't carry any great current. I seem to remember reading somewhere that the thermostats were rated as 5 volt but I can no longer find the spec. I need advice on a suitable replacement thermostat as I am confused as to the different types of thermostats (2-wire, 3-wire, 24V, 240V, etc). I'm happy to consider one of the newer smart thermostats if it would work with the system I have. Thanks in advance.