Thermostat displays E9 and cannot control the heating load

Safety: This fault involves high voltage. Turn off the breaker and verify power is off before touching the thermostat or wiring.

Steps to troubleshoot E9 (output failure):

• 1. Verify load rating: Check the total wattage of connected heaters and compare with the maximum load rating printed on the Stelpro thermostat. If the load is higher, the output device may have failed from overload.
• 2. Inspect wiring: Remove the thermostat from the wall and inspect the line and load terminals for signs of overheating, melted plastic, or burnt smell. Correct any loose or discolored connections.
• 3. Test heater circuit: With the thermostat removed and power OFF, use a multimeter to check continuity of the heater load wires. An internal short in the heater can damage the thermostat output.
• 4. Bypass test (advanced, with caution): With power OFF, temporarily connect the line and load wires together using an approved wire connector, then restore power briefly to confirm the heater operates. Do this only if you are qualified and never leave it bypassed. If the heater works, the thermostat output is likely defective.
• 5. Replace thermostat: The triac or relay is not field-replaceable on Stelpro smart thermostats. Replace the thermostat and, if the load is near the maximum rating, consider using a Stelpro relay or contactor controlled by the thermostat.
• 6. Add surge protection: Install surge protection on the heating circuit to reduce the risk of future output failures from voltage spikes.

Warning: Never operate the heating circuit with the thermostat bypassed except for brief testing under supervision.