Cause of error code A18

High Temperature opens during normal operation.

Solution for error code A18

1. Disconnect harness from High Temperature Supply Switch and Control Module J13. Check continuity of both purple wires. Continuity available from both purple wires? 
Yes: -> 2
No: Replace wire)s) 

2. Is supply water temperature less than 185ºF ( 91ºC)?
Yes: -> 3
No: -> 5

3. Is high temperature supply switch open? 
Yes: Replace high temperature supply switch
No: -> 4

4. Measure resistance across high temperature supply switch terminals 2 and 4? Does resistance match supply water temperature? 
Yes: Replace control module
No: Replace high temperature supply switch.

5. Is high temperature supply switch open? 
Yes: Replace high temperature supply switch
No: Replace control module