William Rahm

Our heat pump is an AqualCal, model T-115 that has heated our 14,500 gallon, in ground pool flawlessly for 16 years.  

When I turned the heater on for the first time this season, I set the thermostat to it's maximum setting intending to lower the setting when the temperature reached 83 degrees.  The heater ran continuously until the water temperature reached 83 degrees as determined by the pool thermometer.

Unfortunately, I was not aware the pool thermometer was defective and was reading 10 degrees low. So, the actual water temperature was 93 degrees when measured with an accurate thermometer.

When the water temperature reached 93 degrees, the heat pump began cycling off and on at approximately a 4 to 6 minute interval with the thermostat on the heater set to maximum. 

When the heater is running I can reduce the thermostat setting approximately 50% and the heater will turn off.  However, if I leave the thermostat set to the maximum setting the heater will run with the water temperature at 93 degrees for 5 minutes then will cycle off and on. 

I am not suggesting I want the water temperature set to 93 degrees however, I don't recall the heater ever cycling before and I wondered if there is a high water temperature shut off switch that is causing the heat pump to cycle independent of the thermostat, or if the cycling is an indication that something is wrong or starting to go wrong. 

I should mention this is the first year we have left the vinyl bubble cover on the pool when we started using the heater. Also, the power and flow lamps are lit when the unit it running and the cycling occurs when using either heater thermostat.

Thank you in advance for your advice..

Bill Rahm  
It's either the control board or water sensor that causing the problem.
Thank you for your reply.

<quote> It's either the control board or water sensor that causing the problem.

By "water sensor" I suppose you mean the thermostat. 

If I understand the unit is suppose to work correctly, the thermostat (water temperature sensor) adjust the water temperature that the unit will stop running.  When the water temperature drops below the thermostat set point by some amount, the unit will start running again. 

As I mentioned in my previous post, both thermostats will turn the unit off when I reduce the adjustment approximately 50% from maximum while the unit it running.  I guess it is possible both thermostats are defective. However, I believe that is unlikely.

Yesterday, I set the thermostat to 50% and the unit cycled normally.  It turned on when the water temperature cooled and turned off when the water temperature reach the set point. There was a 2  degree differential.

I also measured an 11 degree difference between the in and out air temperature at the unit and a 2-3 degree water temperature difference between the incoming water temperature and water temperature at the skimmer.  According to the Owner's Manual,  both those parameters are normal.

It is only when the thermostat is set to maximum and the water temperature reaches 93 degrees that the unit cycles on and off at a 3 to 6 minute interval. 

I suspect the short cycling may have nothing to do with water temperature.  Or, there is a maximum water temperature sensor that is independent of the thermostat setting. 

If there is no maximum water temperature limit and the thermostats are working correctly as they appear to be,  I fail to understand what is causing the short cycling.  

If a component on the control board is defective, why would the unit cycle on and off normally when the thermostat is set lower then the maximum setting?

Is it possible the air temperature sensor that is located on the outside of the condenser is involved?

At this point, I think it is unlikely that both thermostats are defective. 

I don't mind replacing the control board if it is defective but I would like to rule out other possibilities before doing so or at least hear from someone who has experienced the same symptoms and how their situation was resolved.

Currently, the unit is maintaining a 85 degree water temperature and cycling normally with the thermostat set to approximately 50%

I would deeply appreciate it if someone would explain to me how/why the control board would cause the heat pump to cycle at a 3 to 6 minute interval ONLY when the thermostat is set to maximum and the water temperature is 93 degrees? 


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