Safety first: No mains work is required; handle batteries carefully.

Steps to check:

Confirm batteries: Use fresh alkaline cells of the correct size (AA or AAA as specified). Avoid rechargeable NiMH cells unless explicitly supported.
Check polarity: Ensure each battery is oriented according to the +/− markings in the compartment.
Clean contacts: If there is any white or green corrosion, gently clean the contacts with a dry cloth or fine abrasive. Do not use water.
Flex test: With batteries installed, gently press on the battery holder area. If the display flickers, internal solder joints may be cracked.

Resolution: If the thermostat remains dead with known-good batteries and clean contacts, replace the thermostat head.

Battery-powered Salus thermostat will not turn on; screen remains off even with new batteries.

Possible Causes