Thermostat shows E8 and may shut down heating or cooling due to detected high internal temperature.

Safety first: Do not attempt to operate the system if the thermostat or wall feels hot to the touch. Turn off HVAC power if you suspect overheating.

• Check location: Ensure the Payne smart thermostat is not directly above a supply register, radiator, or other heat source. If it is, relocation to an interior wall away from heat sources is recommended.
• Inspect wall cavity: Remove the thermostat and feel inside the wall opening. If it is very warm, there may be hot plumbing, a flue, or attic air leakage behind the thermostat. Seal the opening with non‑flammable insulation or foam as appropriate.
• Ensure ventilation: Confirm that the thermostat backplate is mounted flat and that ventilation slots are not blocked by paint or wallpaper.
• Power cycle and monitor: After addressing environmental causes, power cycle the system and monitor the thermostat temperature reading. If E8 recurs in a normal environment, the internal components may be overheating due to a fault.
• Replace thermostat if needed: Persistent E8 with normal ambient conditions indicates a failing thermostat. Replace with a new Payne smart thermostat and verify proper mounting.