GB1377075A - Thermostatic arrangement - Google Patents

Abstract

1377075 Thermostatic controls for boilers HARFORD-UNICAL Ltd 12 Sept 1972 [16 Sept 1971] 43209/71 Heading F4B In a domestic boiler having a control level thermostat and a high level safety thermostat, the thermostats and other controls are so arranged that a shutdown due to the safety thermostat operating when there is an overshoot on the control thermostat is distinguished from a shutdown due to operation of the safety thermostat after failure of the control thermostat. In one embodiment, Fig. 1, the control thermostat 1 has normally closed contacts in series with the normal burner controller 2, and the safety thermostat has normally closed contacts 4 in series with a flame detector 3 connected to the controller 2. If the control and safety thermostats both operate, the boiler is shutdown normally, but if safety thermostat operates while the control thermostat contacts remain closed, the action is similar to that produced if the flame is not established. In other arrangements, the normally closed control thermostat contacts are connected in series with a change over contact of the safety thermostat, so that if the safety thermostat operates while the control thermostat remains closed a thermal switch or latched relay is operated to light a signal lamp and produce a lock out until a reset pattern is pushed. In an arrangement comprising changeover contacts on the control thermostat 15 and on the safety thermostat 16 are connected in series, Fig. 3, with the normal controller 22, in their normal position, and the normally closed contacts 17 of a latching relay operated by a coil 19 are connected in series with the thermostats. An alarm light 21 bridged by reset button 20 and relay coil 19 are energized by the operation of the safety thermostat 16 while the control thermostat has not operated. The time delay in the relay must be longer than that of the safety thermostats. Other arrangements avoid the necessity for different time lap in the relays and thermostats.