Problem with PT2 thermostat?

I have no idea how your system is piped or wired or what valves or controls you may have, but it is possible that your PT2 roomstat controls the heating through a zone valve, you may be able to see it on the pipework somewhere?? This valve has a motor in it which opens the valve to let hot water circulate in the radiators, when the valve fully opens, an internal switch pes power to the boiler/pump. If this motor fails you will have no heating. The motor is easily replaced, but you first need to diagnose the problem, best get a heating engineer to check.