Pentair mastertemp 400 heater issue


Mar 26, 2017
I received an E05 error on my Pentair Mastertemp 400 heater. It is about 8 years old and hasn't been used that often. At first heater would stay on about 12 seconds before shutting down. I replaced the stack flue sensor and now it runs about 30 seconds and shuts down. I've got it apart and the interior doesn't appear to be very dirty. Please help!!

Pool Clown

In The Industry
Sep 5, 2008
Silicon Valley, CA
I just attempted to check the thermal regulator, however with much difficulty all that came out was the spring. Please help?
That is a symptom of a broken manifold by-pass valve P/N 77707-0001. P/N 460923 would be for the ASME old heater design prior to 10/2012.

NOT the end of the heaters' life, but a project that you may, or may not want to tackle on your own...


TFP Expert
In The Industry
Jul 6, 2011
When you take the unit apart, it will be pretty obvious as how it goes back together. You can easily find directions online just like Pool Clown showed you.

Make sure to get a new thermal regulator with clip. Also replace the orings and the gasket.

Good luck.