Spa builder spa error code 126

Might help to know the model, but with a brand new installation, I'd call the installer out to troubleshoot.

I don't think that 126 is an error code but more likely it's showing that as the temperature.

A new temperature probe will probably be the fix.

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

These codes indicate that you have a bad temperature sensor. Once replaced, the error codes will go away.
This is an easy do it your self project, or it may still be under warranty. Check with your install date; if you have installed the heater 1 year or less (single piece of Pentair Equipment) or if you recently built the pool and installed 3 seperate pieces of Pentair Equipment, your warranty is extended to coverage for three years.

www.cheappoolproducts.com/.../Max-E-Therm-manual.pdf - United States
https://www.gpspool.com/.../Sta-Rite/Tech%20-STA-%20Servicing%20the%20Heater%20Control%20Board%20%u2013...
Those manual should sort you out.

dont know what heater yuo got may be a board or temp sensor also post if automatic control

The 126 is not an error code, but it maybe the temp of the water that the heater is reading. If the heater thinks the water is 126 degrees, it will not start at all.

If the heater is reading the wrong water temp, the problem is the Thermister, which is the sensor that is suppose to read the water temp. You will need to replace this sensor in order to correct the problem with the heater. It is really easy to do!

If you have a manual for the heater, if you go to the Replacement Parts Listing for the Electrical System, page 53 in the online version, the Thermistor is Item #9. It goes into the left side of the manifold in the to place, between the first two manifold bolts.

I am not sure if you have solved this issue, or not, but here is one idea. When you turn on the heater, it is reading the temp at 125/126 correct? IF this is what the heater is reading, then the problem is the Thermistor,or temp sensor, and is very easy to replace.

If you have an Owner's Manual, there are part numbers and instructions on how to replace the Thermistor. If you do not have one, follow the link below and it will take you to one online:

http://www.pentairpool.com/pdfs/MaxEThermOM.pdf

This is a bad thermister or heat sensor. It mounts in your water manifold and if it goes bad no error will show. The bad sensor is telling the heater that the water is to hot and it wont let the heater fire. This is a farley inexpensive part and easy to change out. With a new one it should read the proper temp and call for heat then fire the heater. Good luck.