Primary controller

Heating · Oil Furnaces · printed page 139 (PDF page 140)

Book index entries

Oil Furnace – Primary Control Oil Furnace – Stack Controller Oil Furnace – Stack Relay Primary Control for Oil Furnace Stack Controller for Oil Furnace Stack Relay for Oil Furnace

Text in the illustration

chimney
oil furnace exhaust flue (vent connector)
heat probe
primary controller (primary relay or stack relay)
reset
exhaust from furnace
chimney cleanout
the primary controller checks the exhaust flue for heat - if it doesn't find any, it assumes that the oil burner is not igniting properly and shuts it down
the reset button should only be pressed once if the burner fails to come on (otherwise unburned oil will accumulate in the combustion chamber)
the illustration shows an older setup - most modern oil burners have a photocell on the burner to verify ignition

Generated explanation

The illustration shows an older oil-furnace primary controller, also called a primary relay or stack relay, mounted on the exhaust vent connector at a chimney. A heat probe extends into the connector, and an arrow indicates exhaust flow from the furnace toward the chimney. The controller has a reset button, and a chimney cleanout is shown below the connector. Annotations explain that the controller shuts the burner down if it does not detect exhaust heat, and warn that repeated resets can accumulate unburned oil in the combustion chamber. A note contrasts this older arrangement with modern oil burners that use a photocell to verify ignition.

Related illustrations

0834

Primary controller

· p. 140

The illustration shows an older oil-furnace primary controller mounted on the exhaust vent connector where it enters a chimney. A heat probe projects into the connector to detect heat from furnace exhaust, and the contro