Heater temp is 78 the water temp 68 how do I reset heater temp to match pool temp.

This is not an error code. 128 r13 is the normal programming or software version for your model. you need to press the spa on button again, make sure the temp set point is higher then the actual water temperature

What make/model?

Temperature Thermistor is bad

Standard 10K ohm sensor appears to be compromised. Replace it.
You have one for water temp, one for air temp, and one for the solar if you have one.

Yes there is, but only a service technician is allowed to adjust it. However, the fact that you are only reaching 78 degrees makes me think something else is wrong.

Your bypass valve is probably the culprit. It is located where the Pipes enter the heater. It has a spring on it that is thermally activated to open and close. This allows the right amount of water to pass through the heater. Too much water and the water will not heat up. Too little water and the heater will vibrate and howl!

You could also have a faulty thermostat.

Also, always use a heater blanket when trying to heat a spa or pool. It will save you lots of money and time! And they are cheap!

if the heater tests out good, you most likely have a problem with the water temperature sensor. Make sure that the temp readout matches the actual water temp.. Sometimes the heater will think that the water is up to temp because the temp sensor is feeding the circuit board bad info. Check sensors, replace as necessary.

where the thermostat is located, the pump is not circulating the water

what is the tem at the heater do you have a automatic control what is the temp here may need new temp sensor but dont have all info

if it is around 93-97 degrees outside,thats all the cool your going to get