Thermostat emits a buzzing or high‑pitched noise during operation.

Safety: Low‑voltage only at the thermostat, but turn off power at the breaker if you remove it from the wall for extended inspection.

• Step 1 – Confirm source: Place your ear close to GLAS to confirm the noise is from the thermostat, not the furnace or ductwork.
• Step 2 – Reseat thermostat: Remove and firmly reattach GLAS to the wall plate to reduce vibration.
• Step 3 – Isolate interference: Move any switching power supplies, Wi‑Fi access points, or other electronics away from the thermostat.
• Step 4 – Replace thermostat: If the noise persists and is clearly from GLAS, an internal component is likely vibrating or failing. Replace the thermostat.