E2
Saunier Duval Server Communication / TLS Error

Thermostat shows E2 and mobile app cannot control it remotely, though Wi‑Fi appears connected

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Possible Causes

Outdated thermostat firmware incompatible with current cloud API, DNS issues on home router, Firewall blocking outbound ports used by Saunier Duval servers, Incorrect time/date causing certificate validation failure

How to Fix / Troubleshooting

Safety: No electrical work required.

  • Check time and date: Ensure the thermostat shows the correct time and date; enable automatic sync if available.
  • Firmware update: From the app or thermostat menu, check for and install any available firmware updates.
  • Router DNS: Set your router to use standard DNS servers (e.g., your ISP or public DNS) instead of custom blocking services.
  • Test with hotspot: Temporarily connect the thermostat to a mobile phone hotspot. If E2 disappears, the issue is with your home network configuration.

If E2 continues across different networks, contact Saunier Duval support for cloud-side diagnostics.

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Repair Difficulty

Easy 2/5
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