Safety thermostats ST-1 and ST-2 can be used in directly or indirectly connected district heating systems where extra safety is required. ST-1 incorporates a thermostat (TR) and a safety monitor (STW) with automatic reset. ST-2 incorporates a thermostat (TR) with automatic reset and a safety limit cutout (STB) with manual reset. If ST-1 or ST-2 is used together with an AMV(E) 13, 23, or 33 three-point controlled actuator, the safety monitor (STW) or safety limit cutout (STB) releases the spring return function for forced closure of the motorized control valve. The safety thermostats are approved in accordance with DIN 3440 with the following DIN Register Nos.: ST-1: TR STW 1175 05 ST-2: TR STB 1176 05