Heater vibrates or hums loudly when heating.

Safety first: Turn off power before tightening any mounting hardware. Avoid placing hands near hot surfaces.

Steps:

• Check mounting: Ensure wall brackets and anchor bolts are tight and appropriate for the heater’s weight (especially for large Tesy vertical models).
• Isolate pipes: Add rubber or foam pipe supports where pipes contact walls or the heater casing to reduce transmitted vibration.
• Inspect element: If noise is accompanied by popping, inspect for scale and descale or replace the heating element assembly.
• Flow adjustment: If noise occurs mainly when drawing hot water, slightly reduce flow at the nearest valve to see if vibration decreases.