Boiler Startup Sequence

Briefing

A gas-fired boiler uses a strict startup sequence to ensure safe ignition. The purge fan must run for 30s while PURGE_PRESSURE_OK is confirmed. Then a pilot valve opens and ignition energises for 5s — FLAME_SENSOR must confirm ignition within this window. If flame is confirmed, the main fuel valve opens and the pilot is closed. Loss of flame during run latches a fault. Low water also latches a fault.

Objectives

• Start sequence: PURGE_FAN on for 30s with PURGE_PRESSURE_OK confirmed
• After purge: PILOT_VALVE + IGNITION on for 5s — FLAME_SENSOR must assert
• Flame confirmed: MAIN_FUEL_VALVE on, PILOT_VALVE off, IGNITION off, BURNER_ON_LAMP on
• Loss of FLAME_SENSOR during run latches FAULT_LAMP and shuts fuel
• WATER_LEVEL_OK must be true before and during run; loss latches FAULT_LAMP
• ESTOP or STOP_PB at any time shuts all outputs and latches fault if mid-sequence

I/O Table

Your program will be tested against:

All test cases run automatically when you submit. Assertions are hidden until you pass.

1. #1Purge fan starts on START_PB with water OK

   START_PB while WATER_LEVEL_OK -> PURGE_FAN energises

2. #2Ignition fires after 30s purge

   After 30s purge with pressure OK, PILOT_VALVE + IGNITION energise

3. #3Flame confirmation opens main valve

   FLAME_SENSOR during ignition -> MAIN_FUEL_VALVE on, pilot off

4. #4ESTOP shuts all outputs and latches fault

   ESTOP during run -> all outputs off, FAULT_LAMP on