Hot tub issue when using jet pump

Ukiwis

Active member
Jul 22, 2018
41
California
My MasterTemp 250 heater works fine and heats the hot tub to the set point (104F). It cycles on and off as the temperature changes while it's being used. The problem I have is only when the jet pump is running.

When the jet pump is turned on, the temperature being reported slowly increases to around 109F, even though the water temperature slowly drops. Because it's reporting higher than the set point the heater doesn't come on and the water temperature slowly drops away. It's noticeably cooler than 104F.

Once the Jet Pump is turned off, the temperature correctly reports and the heater fires up again.

Unless someone has a better idea I think I'll replace the thermistor and the high limit switch.
 

Ukiwis

Active member
Jul 22, 2018
41
California
I think I might have figured this out.

A week or so ago I had gone into the "VSP Setup" menu and lowered the MAX speed from 3450 down to 2000. I thought that running the filter pump at a lower speed would result in electric savings.

I've just gone back in and and reset it back to where it was and everything now appears to be normal again. With the jet pump running the temperature drops a few degrees, firing the heater back up again till it reaches the set point.
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
12,750
Northern NJ
FYI, your Aqualink RS does not use the thermistor in the heater for temperatures control. The Aqualink has its own thermistor inserted in a return PVC pipe.

When under control of the Aqualink the heater thermistor displays the temperature on the heater control panel but does not control the heater cycling.
 

Ukiwis

Active member
Jul 22, 2018
41
California
FYI, your Aqualink RS does not use the thermistor in the heater for temperatures control. The Aqualink has its own thermistor inserted in a return PVC pipe.

When under control of the Aqualink the heater thermistor displays the temperature on the heater control panel but does not control the heater cycling.
Thanks, I did not know that.