Boiler locks out with E06, temperature reading is erratic or out of range

Safety: Turn off power and allow the boiler to cool before touching any piping or sensors.

• Step 1 – Locate the supply sensor: On Triangle Tube boilers, the supply NTC is typically clipped or threaded into the supply outlet pipe inside the cabinet. Identify the small probe with two wires.
• Step 2 – Inspect wiring: Check the sensor connector and wiring back to the control board. Reseat the plug and look for corrosion or broken insulation.
• Step 3 – Check sensor mounting: Ensure the sensor is firmly attached to the pipe or properly inserted into its well. A loose sensor can read incorrectly.
• Step 4 – Power cycle: Restore power and reset the boiler. If E06 returns immediately, the sensor is likely defective.
• Replacement: Shut power off again, remove the old sensor (be prepared for a small water leak if it is a wet-well type), install the new Triangle Tube-compatible NTC sensor with proper sealing, reconnect wiring, and refill/bleed if needed.
• Call a technician: If replacing the sensor does not clear the error, the control board may require professional diagnosis.