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Right Card. Right Timing. In Stock.

Combustion Safety Relays \ Honeywell 7800 Series Burner Management Systems

Combustion Plus stocks 22 Honeywell ST7800 purge timer cards covering the full range of prepurge timing for 7800 Series burner control relay modules. A missing or wrong-timed purge card prevents a burner from completing its startup sequence. Keeping the correct replacement on hand avoids shutdowns that wait on shipping.

ST7800A cards provide prepurge timing from 10 seconds to 30 minutes
ST7800C cards are for use with the RM7838C relay module only
Both series plug directly into 7800 Series relay module subbases

How Do Honeywell ST7800 Purge Timers Protect Industrial Burner Startups?

Before a burner ignites, the 7800 Series burner control requires a timed prepurge cycle to clear unburned fuel from the combustion chamber. The ST7800 purge card sets that timing. If the card is missing, the relay module will lockout rather than proceed to ignition, which is correct by design but stops production. Selecting the right prepurge duration is application-specific and code-driven, not a generic default.

Plug-in card format allows field selection of prepurge time without wiring changes
ST7800A cards compatible with RM7800, RM7838, RM7840, RM7850, RM7865, and related modules
Prepurge timing set by card model, not adjustable after installation

Why Do Maintenance Teams Source Purge Timer Cards Through Combustion Plus?

Combustion Plus is a factory-authorized Honeywell Thermal Solutions representative stocking both ST7800A and ST7800C series purge timer cards. When a 7800 Series burner control locks out with a missing purge card fault, the fix is a direct swap. Local inventory means same-day resolution rather than a multi-day sourcing delay.

Authorized Honeywell Thermal Solutions rep with ST7800 replacement cards in local stock
ST7800A and ST7800C cards stocked across multiple prepurge time increments
Combustion Plus carries the full Honeywell 7800 Series ecosystem in one catalog

FAQ

What is the difference between the Honeywell ST7800A and ST7800C purge timer cards?

The ST7800A series works with most 7800 Series relay modules, while the ST7800C is designed specifically for the RM7838C relay module.

What prepurge timing options are available in the Honeywell ST7800A series?

ST7800A cards are available in prepurge durations from 10 seconds through 30 minutes, with multiple time increments stocked.

Can an ST7800 purge timer card be adjusted in the field after installation?

The prepurge time is fixed to the card model and cannot be adjusted after installation; selecting the correct model for your application is required.

What happens if a purge timer card is missing from a Honeywell 7800 Series relay module?

The relay module will go to lockout and prevent burner startup, which is the designed safety response to a missing or defective purge card.

Find the Right Purge Timer Card for Your Burner Control System

Combustion Plus stocks Honeywell ST7800A and ST7800C purge timer cards so your 7800 Series burner controls stay operational. Search by part number or call (248) 549-1703 to confirm the right prepurge timing for your application.