Pentair Mastertemp 250 Won't Stay Running

I have a 4 year old Pentair Mastertemp 250 that won't stay running. When I turn it on, I can hear it start up then I can hear the burners light. Then after a second or two, I can hear an audible sound of something "winding down". Then an audible click. At that point the temperature readout on the control panel increases up 4 or 5 degrees 1 degree at a time then rolls back down to where it was initially set at. It will go through this same process again and again after it sits for 10 to 15 seconds. There are no other error codes or lights on other then the heating light flashing. I've attached a video of what's happening. The background noise is my pump running right next to it. I'm not sure what to check first. The troubleshooting guide wasn't very helpful without any warning codes.
 
I don't have your model of heater, but what you are describing seems pretty odd. I presume the temperature display is supposed to be the temperature of the water coming into the heater, right? If that's the case, then it sounds like that is rising immediately (which it shouldn't) perhaps above the temperature set point, and then removing the demand for heat. If you raise the target temperature, does the flame burn longer?
 

Is it the same heater from this thread?

Do you have pictures of everything?

You can post video on YouTube and post a link here.
 
Remove the thermal regulator and see if it is opening all the way.

Try running the heater without the thermal regulator.

Only do this as a test.

Don't leave the thermal regulator out for an extended period of time.

 

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Do you have pictures of the entire system?

Did you remove the thermal regulator to see if it is opening all the way?

Did you try running the heater without the thermal regulator?
 
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