Solid fuel boiler firing control thermostat - has safety device to prevent overheating by overriding action if thermostat fails

摘要

The boiler is fitted with a thermostat to control the water temperature. A capsule (2) inside the housing (1) contains a liquid which expands when heated to the control temperature so that the capsule and its attached bracket (13) are forced downwards against the force of a spring (6). The boiler air inlet flap is normally held open by a chain (9) attached to a lever (8'). The downward movement of the capsule and bracket removes the support from this lever so that the air flap is no longer supported and swings to the closed position. The spring abuts against a ring (15) of a material which softens at a temperature higher than the maximum permissible water temperature. In the event of a thermostat failure this ring collapses and allows the air control flap to close.