Safety first: Disconnect power before handling electrical connections.

Check adapter: Replace the external Viessmann power adapter with a known-good unit of the correct rating.
Inspect connectors: Ensure the low-voltage plug is firmly seated and free of corrosion.
Secure cable: Route the cable away from sources of electrical noise (e.g., pumps, motors) and avoid sharp bends.
Board check: If flickering persists with a new adapter, the control board's voltage regulator may be failing and should be replaced.

Softener display backlight flickers or dims intermittently

Possible Causes