Boiler display is on but there is no response to a call for heat; status shows 'Standby' even when heat is needed.

Safety: Turn OFF power before working on low-voltage circuits.

Steps:

• 1. Verify thermostat operation: Raise the thermostat setting and listen for a click. Replace batteries if applicable.
• 2. Check call-for-heat terminals: At the Raypak control, measure or test for continuity across the call-for-heat terminals when the thermostat is calling. Repair wiring if open.
• 3. Review control settings: Ensure the boiler is not in 'Off' or 'Manual' mode and that any external enable contacts are configured correctly.

If the boiler still does not recognize a call for heat, the control input or external interlock device may be faulty and require professional diagnosis.