🔍 Key Concepts

• Automatic boiler programmed control sequence — what happens specifically during the pre-purge period before light‑off • Combustion air proving — how the system makes sure there is enough forced draft air flow before allowing ignition to proceed • Difference between conditions checked for air side (purge/safety) vs fuel/water side (firing operation)

💭 Think About

• Think about the purpose of the pre-purge period: what unsafe condition is it trying to remove or prevent before any fuel is admitted? • Which of the listed conditions would be most directly related to making sure the furnace is properly purged with air and that combustion gases can be safely cleared out? • Ask yourself: at this point in the sequence, has fuel been introduced yet, and which sensors would logically be interlocked before fuel is allowed on?

✅ Before You Answer

• Verify which parameters the control system must prove during pre-purge: air flow and the correct position of the air path components (like dampers or registers) • Confirm that fuel- and water‑side conditions are typically interlocked closer to or during the actual light‑off/firing phase, not during the initial pre‑purge air sweep • Check whether the correct damper position for purge is specified as open vs closed in standard boiler safety logic and NFPA‑style purge requirements (more open or more closed for safe purging?)