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: Locate the low-voltage terminals on the Triangle Tube control board. Confirm that thermostat or external control wires are connected to the correct terminals as per the wiring diagram.
• 2. Inspect cable: Follow the thermostat cable and look for staples through the wire, cuts, or splices that may be shorting the circuit.
• 3. Test thermostat: At the boiler, temporarily jumper the thermostat terminals (e.g., TT) to simulate a call for heat. If the unit responds normally, the thermostat or its wiring is suspect.
• 4. Check control settings: Enter the installer menu (refer to the Triangle Tube manual) and verify that the control is configured for the type of external control you are using (on/off thermostat, outdoor reset, etc.).
• 5. Replace faulty components: Replace a defective thermostat or damaged cable. If the control board does not respond even with a direct jumper, the board may be faulty and should be replaced by a professional.