Maatertemp 400 will not progress past 888 display


New member
May 26, 2020
Hi. I'm hoping to get some help with my master temp 400. When the heater turns on the display will not progress past displaying 888. The service system light is on. I was thinking it was the pressure switch so I replaced that, but it did not fix the problem. I have turned my filter to recirculation and back washing to see if I made any difference but it did not. Any ideas?


TFP Expert
Mar 2, 2011
There should be a sticker with a barcode and the manufacturing date.

In any case, I suspect that the circuit board is probably bad.

If the membrane pad is in poor condition, replace that at the same time.

When is the last time that the heater was running properly?