Honeywell ST7800C1011 prepurge timer module 20 sec

The Honeywell ST7800C1011 is a prepurge timer module with a 20‑second timing period, belonging to the family of burner control components classified as industrial controllers. In a burner management system, the burner control (flame safeguard) orchestrates the ignition sequence, and prepurge is the step where the fan runs to clear the combustion chamber before fuel is admitted. Parts of this type are plug‑in modules that determine the duration of the prepurge phase. They are matched to a specific control base or chassis and are not interchangeable across different control series even within the same brand. Selecting a prepurge timer module requires exact knowledge of the burner control series designation and the required timing period. The timing must match the appliance design: too short a prepurge risks incomplete air purge, too long is unnecessary and may cause nuisance cycling. This module is normally installed inside the control panel of a burner or boiler and connects to the main control board via a plug or terminal pattern. When replacing a prepurge timer, verify that the replacement unit is the correct series and that the timing value—here 20 seconds—corresponds to what the burner manual specifies. A mismatched prepurge timer can prevent the burner from starting correctly or create a safety concern, as the safety sequence depends on accurate timing.