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H2O / Error 4 / Water Prime Failed in Spas - What It Is and What to Check

What is an "H2O" Error or "Water Prime Failed" or "Error 4" in the spa or hot tub? 

The spa controller has either an Optical water sensor, or a temperature probe style water detector. With an H2O, Error 4, Water Prime Failed error, it has detected there is a lack of water in the heater itself, or a sensor may be faulty. 

Parts that may be faulty:

Steps to Test for an H20 error or Error 04 :

  1. Check to make sure that the spa is filled with water to the correct level.
  2. Remove Filters. Blocked filters from clarifier use or dirty filters are the number one cause of H20, Error 4 and Water Prime Failed errors.
  3. Check heater is fully primed, with no air. Bleed air if necessary.
  4. Check heater is installed correctly.
  5. Run the pump, and ensure there is adequate water flow. Repeat running the pump several times.
  6. Replace the optical sensor.

For Davey Spa-Quip controllers, reset the controller using the touchpad.

  • SP400, 500, 600: Press UP, DOWN, PUMP buttons simultaneously.
  • SP800, 1200: Press the top four buttons simultaneously.

For all other controllers, turn off power for 5 seconds and restart.

How to Fix an H2O / Er 4 Fault:

If the error continues to occur, you may have a faulty sensor or controller. Most of the time, it's the sensor itself. With poor water quality, age, improper installation, and rarely to a defect, optical sensors can fail. Calcium hypochlorite or high calcium levels can also coat optical sensors, causing them to fail. 

Ensure you are not using Bromine, Trichlor, Calcium Hypochlorite, and that your pH, Total Alkalinity and Sanitiser levels are within appropriate ranges.

The Spa Controller, Heater, and Sensor should be tested by a qualified & experienced person. When the fault is found, the part may be replaced, or repaired. 


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