Raypak LIMIT SEN

What does Raypak LIMIT SEN mean?

The controller has detected an abnormal condition from the high limit temperature sensor and can no longer rely on it to protect the heater against overtemperature. Because the high limit is a safety sensor, the control flags LIMIT SEN and may lock out, requiring the maintenance person to manually reset it after the sensor and its wiring have been corrected.

Symptoms

• LIMIT SEN displayed as the active error on the controller
• Heater lockout requiring a manual RESET
• Red fault LED indication on the PIM
• Display reverts to normal only after the condition is corrected

Common causes

• Failed or out-of-range high limit sensor
• Damaged or loose high limit sensor wiring
• Poor connection at the PIM
• Sensor resistance outside the published values

Diagnostic steps

1. 01

   Check the high limit sensor and its wiring

   Per the manual, inspect the high limit sensor and its wiring for damage, looseness, or corrosion.

2. 02

   Verify sensor resistance

   Compare the measured sensor resistance against the Sensor Resistance Values table for the current water temperature and replace the sensor if out of range.

3. 03

   Inspect PIM connections

   Confirm the high limit sensor leads are securely connected at the PIM with no loose or backed-out pins.

4. 04

   Reset the control

   After correcting the sensor and wiring, push and release the RESET button to clear the fault.

5. 05

   Observe operation

   Monitor several cycles to ensure correct operation and no reoccurrence of the fault.

When to call a professional

This is a safety sensor whose failure can defeat overtemperature protection, so accuracy matters. Diagnosis needs a meter and the resistance table, and service is performed near hot water, gas, and live wiring with the manual's danger and warning conditions to verify first. If you cannot confirm the heater is depressurized, cooled, gas-off, and de-energized, have a qualified Raypak service technician perform the repair.