E12
Stelpro Backup Power / Real-Time Clock Failure

Thermostat shows E12 and schedules or settings are lost after power outages

Advertisements

Safety Warning

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

Advertisements

Possible Causes

Failed backup capacitor or coin-cell on Stelpro main board, Corrupted RTC firmware, Excessive power interruptions, Manufacturing defect in clock circuit

How to Fix / Troubleshooting

Safety: Turn off power at the breaker before removing the thermostat from the wall.

Steps to troubleshoot E12 (RTC/backup failure):

  • 1. Confirm symptom: Note whether time and schedules reset after every power outage or only occasionally.
  • 2. Check firmware: Use the Stelpro app to verify and update firmware to the latest version, which may correct RTC handling.
  • 3. Minimize power interruptions: If your home experiences frequent outages, consider installing an uninterruptible power supply (UPS) on the heating control circuit (for low-voltage systems) or addressing utility issues.
  • 4. Inspect internal backup component (advanced): With power OFF and thermostat removed, inspect the PCB for a small coin-cell battery or supercapacitor used for backup. If visibly leaking or swollen, the board should be replaced.
  • 5. Replace thermostat: If E12 persists and the clock cannot retain time through short outages, replace the thermostat under warranty if applicable.

Note: Some Stelpro smart thermostats rely on cloud time sync; ensure Wi-Fi and cloud connectivity are stable.

Advertisements

Repair Difficulty

Medium 3/5

Required Part

Stelpro Smart Thermostat Main Control Board (RTC/backup circuit)
Check Price on Amazon

We may earn a commission from links on this page.

Advertisements