pentair mastertemp 250 e05


Bronze Supporter
Jan 19, 2013
Haines city, FL

i have read everything i can on this issue i can find. even down to checking the main board to see if it had switched to sf0, it had not.

quick history.
heater is 10 years old. exhaust and intake are clear. no nests inside unit actually pretty clean for 10 years.
the main board was replaced 6 years ago, it vibrated loose and got wet. new board is rev12.

ordered replacement sf sensor. same issue. heater starts, runs for ~30 seconds then shows e05 and the sfs led lights on the main board.

i checked the both old sensor 2.9mohms and new sensor 3.1mohms

both sensors will not show exhaust temp when you hold down pool on button. just goes between 80 and flashing 40.

coils seem to look ok and it is dry in the exchange area.

replacement sensor bad? or main board?

am i missing something obvious? i really don't want to tear this thing completely apart. :)



TFP Expert
Mar 2, 2011
The 80/40 reading and E05 indicate that the board is not getting a reading from the sensor.

It's usually a bad sensor or damaged wires.

If the sensor and wires are good, then the main board is the next thing to replace.

Mastertemp 400 E05 error
Last edited:


Bronze Supporter
Jan 19, 2013
Haines city, FL
following up on this. i replaced the main board with the new and different looking one. it was the issue.

i would venture to say that if you are getting the 80 to 40 temp flashing and you fute stack sensor tests ok. it is the board.

on a side note. i did have to swap the wiring for my pool and hot tub switching, it was working opposite than the old style board.