The Honeywell ST7800A1047 40-Second Purge Timer is used for timing long the purge cycle lasts in HVAC systems. The valve opens for 40 seconds, so combustion gases can safely leave the system. This step is needed to keep heating systems running safely and efficiently. This makes sure time always correct, so gases don’t build up and system works better. Automate the process that helps ensure the system remains safe, efficient, and longevity. Maintain better system performance and efficiency.