I am replacing a cylinder thermostat in a central heating system and would appreciate any wiring advice. The old thermostat is a Satchwell. It is very old, settings in Fahrenheit. It has three connections. One wire is yellow and black sleeved and is connected to the metal thermostat housing (so must be earth). The other two wires are coloured red and blue. Their terminals both go to 240V (wrt earth) when heating is on, both are at 0V when heating off. The new thermostat is a Horstmann HCT2. It has three terminals, com, 1 (call for heat), and 2 (satisfied). Given that the new thermostat doesn't have an earth terminal, can I use the three wires from the old Satchwell? If so, how would they be connected?