I just replaced the heating element on my spa. When I turn it on now, I get an error message "The heater may be dry".
The control unit is a Balboa BP501. The heater unit is a Balboa 15" M7 5.5kW. The spa was not heating. I determined that the old heater element had failed (it measured as no connection). After replacing the heating element (just the heating element, not the whole tube), I now consistently get the heater dry error message. I did not drain the hot tub before replacing the heating element - I just closed the slide valves on either side. They leaked some, but not terribly. This hot tub has a separate circulation pump from any of the main seat jets.
The new heating element measures about 10.5 ohms.
When I first turn on the breaker, the spa goes to the pump priming screen. The first time after replacing the heater, I got some bubbles through when turning on the circulation pump. The circulation pump turns on and has good flow. I loosened one of the temperature sensors on the top of the tube, and water comes out, so the heater tube is definitely full. The filters are clean, the water level is good, the gate valves are open, and I have good flow coming from the heating inlets.
After leaving the priming screen, the spa goes to the main screen. After a few seconds, it reads the water temperature correctly (about 55F). After a few more seconds, the screen indicates the heat is turning on. When it does, I can hear the relay click, and I measure 240VAC at the heating element. Just a few seconds later, the relay clicks back off, and I get the error message.
If I clear the message and wait a little while, it will try again, with the same results.
Powering off the breaker for a few minutes before trying again had the same result again.
I turned the breaker off, and disconnected each of the temperature sensors from the control board. Each one measures about 55k ohms, which seems to be about right for the temperature. After reconnecting the sensors and powering back on, I still have the same problem.
Any suggestions?
Thanks!