diff --git a/api/runtime.php b/api/runtime.php
index 3c3d867..570e33d 100644
--- a/api/runtime.php
+++ b/api/runtime.php
@@ -75,7 +75,9 @@ class runtime extends cora\api {
           (
             $thermostat['sync_begin'] !== null &&
             strtotime($thermostat['sync_begin']) <= strtotime('-1 year')
-          )
+          ) ||
+          // For when merging thermostats and sync_begin is less than first_connected
+          strtotime($thermostat['sync_begin']) <= strtotime($thermostat['first_connected'])
         ) {
           $this->sync_forwards($thermostat_id);