Thermostat displays E15 and refuses to start a firmware update

Safety: No high-voltage work is required. Do not cut power during any firmware process.

Steps to troubleshoot E15 (firmware integrity):

• 1. Check app version: Update the Stelpro mobile app to the latest version from the app store.
• 2. Improve Wi-Fi: Move your router closer or temporarily connect the thermostat to a stronger 2.4 GHz network to ensure a stable download.
• 3. Retry update: Cancel the update, close the app, reopen it, and start the update again. Follow on-screen instructions and avoid using the app for other tasks during the update.
• 4. Verify model selection: Ensure the app has correctly identified your thermostat model; do not attempt to load firmware intended for a different Stelpro device.
• 5. Factory reset (if advised): If Stelpro support recommends it, perform a factory reset and then attempt the update again.
• 6. Contact Stelpro support: If E15 persists, provide them with the model number, current firmware version, and error details. They may provide a special recovery procedure.

Warning: Do not repeatedly force updates if the device reports integrity errors; this can brick the thermostat.