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Basic Boiler Controls Hot water boilers share a common set of devices that insure safe and accurate boiler control. Each of these controls should be checked periodically to insure proper operation and none should be disconnected or bypassed to obtain temporary heat. A pressure relief valve acts as the primary safety device. It has been accurately sized to blow off hot water at a rate greater than the input rate of the burner. Pressure relief valves should be inspected in advance every heating season to insure they will open. Periodic pressure testing done off the boiler is appropriate. The aquastat controls the operation of the burner by shutting it down when operating temperature has been reached. They have a limit setting, usually 180° F, and a differential setting, usually 20°F. On atmospheric gas boilers a rollout switch should be present near the burner tray. This temperature switch shuts off power to the gas valve should flame roll toward the gas valve. The blocked vent switch is a similar type device that helps detect a blocked chimney. Should combustion gas spill from the draft diverter the blocked vent switch shuts power to the gas valve. The gas valve controls the flow of gas, either natural or propane, to the burner. Gas valves provide several functions acting as a shutoff valve, a pilot regulator, a burner gas pressure regulator, and a backup shutoff valve. See Flash Demo |
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