E12 error, unit may not respond to thermostat or may run without proper control.

Safety: Turn off power before working on low-voltage control wiring.

• 1. Verify thermostat wiring: Confirm that thermostat wires are connected to the correct terminals on the Triangle Tube board.
• 2. Inspect cable: Look for staples through the wire, cuts, or shorts in the thermostat cable.
• 3. Test thermostat: Temporarily jumper the thermostat terminals (e.g., TT) at the boiler. If it fires, the thermostat or its wiring is the problem.
• 4. Check control settings: Verify the control is configured for the correct type of external input (on/off, outdoor reset, etc.).
• 5. Replace faulty components: Replace a defective thermostat or damaged cable.
• 6. Professional help: If the board doesn't respond to a jumper, it may need replacement by a professional.