diff --git a/frappy_psi/mercury.py b/frappy_psi/mercury.py
index c033d82..a342a38 100644
--- a/frappy_psi/mercury.py
+++ b/frappy_psi/mercury.py
@@ -375,6 +375,7 @@ class HeaterOutput(HasInput, Writable):
 
 class HeaterUpdate(HeaterOutput):
     kind = 'HTR,TEMP'
+    target = 0  # switch off loop on startup
 
     def update_target(self, module, value):
         self.change(f'DEV::TEMP:LOOP:ENAB', False, off_on)