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The original was posted on /r/homeassistant by /u/Drunk_Panda_456 on 2026-05-18 13:03:55+00:00.
I spent several days debugging what I thought was a code issue with my Home Assistant thermostat automation and finally figured out what was happening. Posting in case anyone else runs into this.
If you’re seeing a cryptic error like:
“Provided temperature X is not valid. Accepted range is X to X”
Here’s what’s going on. Matter communicates in Celsius internally. When HA sends a Fahrenheit setpoint to a Matter thermostat, it converts it to Celsius and your value may land right at or just over the device’s ceiling due to floating point rounding. The action then fails or behaves unexpectedly.
What made it so hard to diagnose was that it didn’t always throw an error. Sometimes it just set the wrong mode, or heat would update correctly but cool wouldn’t. All of it traced back to Matter’s unit conversion hitting that ceiling.
The fix: Back your cool setpoint off by a fraction of a degree until it converts cleanly under your device’s ceiling. The exact value will depend on your thermostat’s deadband and temperature limits.
My setup:
• Honeywell Home X8S connected via Matter
• Home Assistant
• climate.set_temperature action
Hope this saves someone else the headache.