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Thermo Fisher Scientific

Lo P1 Error on Thermoflex 900/1400/2500 Chiller



  • ThermoFlex 900
  • ThermoFlex 1400
  • ThermoFlex 2500


Prerequisite: It has been confirmed that the correct voltage is applied: 115V for a ThermoFlex 900 or 1400; 220V for a ThermoFlex 2500 chiller.
If the Thermoflex 900/1400/2500 chillers displays a “Lo P1” error on the front LCD display, it is possible that air is trapped at the pressure sensor or the pump is cavitating.

Change the Lo P1 pressure setting to 3psi and the delay to 30s. See pages 26-27 of the ThermoFlex Operators Manual linked here: U00933 - Rev. 06/01/07 - ThermoFlex Installation, Operation and Basic Maintenance, excerpt to follow, for steps on how to navigate the Setup Loop to make these changes.

Observe if water flows into the reservoir before the ‘Lo P1” error is displayed.

If water is flowing into the reservoir, follow steps 1-4 to attempt to release the trapped air or debris in the pressure transducer.

If NO water is flowing into the reservoir, follow steps 5-8 to remove trapped air in the pump head or prime the pump.


NOTE: Before proceeding, toggle the rocker switch at the back of the chiller to the off position and unplug the chiller from the wall outlet.

Water is Flowing into the Reservoir

If there is plenty of fluid returning to the reservoir, the pressure transducer may not be reading the correct pressure and is therefore causing the shutdown

1) Remove the Right Side Panel by referencing the steps below or video linked here: How to Remove the Cover on a ThermoFlex 900 / 1400 / 2500 Chiller

    a) Use a Philips head screwdriver to remove the five #6-32 x 1/4" screws indicated in the illustrations below.

    b) Slide the right panel back approximately one inch, then lift slightly from the rear to disengage the panel's two tabs from their slots.

The pressure transducer will be accessible from the right side of the chiller.

2) Disconnect the cable circled below by pulling the tab out gently and pulling up

3) Unscrew the Process Pressure Transducer  and clean the connector of any debris that may have accumulated.


4) Press on the Schrader port core to ensure fluid is coming out


5) Reconnect the Process Pressure Transducer followed by the cable and confirm that the “Lo P1” error no longer occurs. If the problem is not resolved, then replace the Pressure Transducer using this knowledge article as a guide to do so: Pressure Transducer Replacement.

Water is NOT Flowing into the Reservoir
It is possible that the pump is still functional, but the pump head may be air locked or that the pump is cavitating. To remove potentially trapped air in the pump head or to prime the pump, follow these steps. 

1) Purge valve may be stuck

a) Remove the right cover by following the steps in step 1 at the top of this knowledge article. 

b) Tap on the purge valve, pictured below, with a wrench. This may loosen the ball bearing inside if it is stuck. Then loosen the Nut, pictured below, to let out any trapped air. Tighten the nut back up.

2) If step 6 doesn't resolve the Lo P1 issue, try purging air out of the pump by doing the following:

NOTE: this is especially pertinent if the fluid was just changed and a Lo P1 is being display on startup afterwards.

a) Place some rags under the front bottom of the pump head

b) Slowly loosen the nut, circled below, until fluid is coming out but take care not to fully remove the nut. If the nut is fully removed, install and tighten as quickly as possible.



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