This notification means that the Passiv Programmer has lost communication with the Passiv Thermostat. Likely causes for this vary depending on whether your Thermostats are wired or wireless.
If you have wired thermostat(s):
If your wired Thermostat has lost communication with the Programmer, this means something has gone wrong with the wiring between the Programmer and the Thermostat, or there is a fault on the Thermostat itself. Contact your installer to get the wiring professionally checked.
If you have wireless thermostat(s):
The most likely cause for a wireless Thermostat going offline is that it has run out of battery. To bring the Thermostat back online, recharge the Thermostat using the instructions here. If you are still getting the 'Thermostat is offline' error after recharging the Thermostat and putting it back on the wall there may be something wrong with the Thermostat's communications. Please reach out to our support team and we will provide further assistance.