Watlow F4T Install & Troubleshooting  •  35  •  Chapter 5 Troubleshooting
Indication Description Possible Cause(s) Corrective Action
Limit High Sensor input above 
high limit set point 
• Temperature is greater 
than limit set point 
• Limit outputs latch and 
require reset 
• Incorrect alarm set point
• Check cause of over 
temperature 
• Clear limit 
• Establish correct limit 
set point
Loop Open 
Error
Open Loop Detect 
is active and the 
process value did 
not deviate by a 
user-selected value 
in a user specied 
period with PID 
power at 100%.
• Setting of Open Loop 
Detect Time incorrect
• Setting of Open Loop De-
tect Deviation incorrect 
• Thermal loop or process 
is open 
 
• Open Loop Detect func-
tion not required but 
activated 
• Set correct Open Loop 
Detect Time for applica-
tion 
• Set correct Open Loop 
Deviation value for ap-
plication 
• Determine cause of 
open thermal loop: 
misplaced sensors, load 
failure, loss of power to 
load, etc. 
• Deactivate Open Loop 
Detect feature
Loop Reversed 
Error
Open Loop Detect is 
active and the pro-
cess value is headed 
in the wrong di-
rection when the 
output is activated 
based on deviation 
value and user-se-
lected value. 
• Setting of Open Loop 
Detect Time incorrect
• Setting of Open Loop De-
tect Deviation incorrect 
• Output programmed for 
incorrect function 
• Thermocouple sensor 
wired in reverse polarity 
• Set correct Open Loop 
Detect Time for applica-
tion 
• Set correct Open Loop 
Deviation value for ap-
plication 
• Set output function cor-
rectly 
• Wire thermocouple cor-
rectly, (red wire is nega-
tive) 
Ramping Controller is ramp-
ing to new set point 
• Ramping feature is acti-
vated 
• Prole is active
• Disable ramping feature 
if not required 
• Terminate prole if not 
required
Autotuning  Controller is 
autotuning the con-
trol loop 
• User started the 
autotune function 
• Digital input is set to 
start autotune 
• Wait until autotune 
completes or disable 
autotune feature 
• Connect the digital 
input to function other 
than autotune, if de-
sired
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