Nest thermostat: H155: Heat Link went offline, batteries low
Your Heat Link went offline when its batteries were low.
Applies to: Nest Thermostat E with a battery-powered Heat Link. What you see: a code and words.
What Google says to do
- Pull off the Heat Link cover and replace the batteries with new L91 Energiser Lithium AA batteries. Google says not to use regular alkaline batteries.
- The Heat Link should reconnect to the thermostat by itself once the new batteries are in; if not, contact a local pro.
Source
Google’s own help page, read on the date shown.
- Google Nest Help: Troubleshoot Nest thermostat help codes — Nest Learning Thermostat (1st to 4th gen), Nest Thermostat E and Nest Thermostat; H codes only where a Heat Link is installed. support.google.com Checked 2026-09-29.