I replaced the circ. pump 5 months ago, and just drained and refilled the tub. New filter, new high limit thermistor installed after tub was drained. The tub heats up to its desired temp, but after a short time blinking red light comes on. Any ideas?

Hello.
If not fixed yet. Pull filter of the circ pump and see if still continues to trip. If so you can test both thermisters and see what ohm reading you get. There is a graph for different temps, but I would see if they are real close to each other in ohm readings. You could have a bad one from the factory.

Hope that helps.
20+ year tech