The operating control does the day-to-day work: it turns the burner on at the cut-in point and off at the cut-out, or drives the firing rate on a modulating burner. It is set below the high limit, so the limit only acts if the operating control fails. Pressure switches on steam and temperature controls on hot water are the usual operating controls.
Operating control kicks it off at 10 psi and the limit is set at 12, so if we ever hit 12 something's broken.
Also heard as
- operating limit
Do not mix it up with
- High limit: The operating control is meant to act every cycle; the high limit is a backup safety that should rarely, if ever, trip.
Related terms
High limit
A safety control that shuts down the burner if pressure or temperature rises above the normal operating range.
Pressuretrol
Shop name for the pressure switch that starts and stops a steam boiler's burner to hold pressure in a set range.
Aquastat
Shop name for the immersion temperature control that fires and limits a hot water boiler.
Differential
The gap between the point where a control turns the burner on and the point where it turns it off.