Pentair Mastertemp 400 E05 error after other stuff.

MJCP

Well-known member
Sep 14, 2007
138
Michigan
My 3rd season with the Mastertemp 400 started with a major problem. I went trough the troubleshooting guide but tried not to tear the whole thing down to make a simple fix. The guide suggested my problem was the control board. But I noticed the price of the board and decided to do some further checking before spending that kind money. Sure enough checking a few Youtubers, suggested my real problem was the blower Motor needed to be replaced - WHAT? even more money. let me check further. Another youtuber warned if there is water at the bottom of the exhaust flu its time for a new heater (luckily mine was bone dry). Time to take it apart and get a serious look inside. Long story short, inside the electrical box was a mouse nest, and the mouse had done a number on quite a few wires. I'm a capable electronic/electric DIY type but certainly capable of bonehead mistakes, but after rewiring everything and firing it back up everything worked fine and my pool came up from 62 Michigan degrees to my happy 88 f. For 2 days everything was fine except occasionally I would get an E05 error. Since I had seen the flue sensor was a 15$ part I went ahead and ordered one "just in case" it will be here Monday. But yesterday I began having the E05 error constantly. The heater turns on fires up, starts to look good for about 5-10 seconds then shuts down. I pressed the Pool On button and held it to get the temp reading -it starts at 80 then 90 then 99 then stars to jump from 40 to 30 then 40 etc, then shuts off. I am Hoping that the new sensor will resolve this but I am also wondering if someone sees a Bonehead mistake I could have overlooked.
Thanks in advance for your thoughts.
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
18,959
Northern NJ
You get E05 errors from low water flow. Not enough water flowing to absorb the heat so it goes out the exhaust and overheats.

Check your filter pressure, backwash your filter, do a Overnight Chlorine Loss Test and check for algae.

What test kit do you have?

Post your water chemistry.
 
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JamesW

TFP Expert
Mar 2, 2011
19,824
When you get E05 and then 80/40 when you check the stack temperature, that means that the board is not reading the stack temperature sensor.

Usually, it's a bad stack flue temperature sensor or wiring or the board.

If the SFS and wiring are confirmed to be good, replace the circuit board.
 
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MJCP

Well-known member
Sep 14, 2007
138
Michigan
You get E05 errors from low water flow. Not enough water flowing to absorb the heat so it goes out the exhaust and overheats.

Check your filter pressure, backwash your filter, do a Overnight Chlorine Loss Test and check for algae.

What test kit do you have?

Post your water chemistry.
I haven't tested today but my readings have been pretty good so far .
I use The LaMott Color Q test kit (Gift from my wife)
I backwash pretty often, and check the pressure obsessively I will check the output on the returns and see what my flow rate is doing
Thanks for that suggestion.
 

MJCP

Well-known member
Sep 14, 2007
138
Michigan
Just received the new Stack Flow Sensor and installed it. It's been running fine for about 10 minutes so far. The old sensor would fail after only 10-15 seconds. So far so good! Thanks for the help....

PS. Purchased from Pool Guy Supply Inc. $14.99 free shipping USPS. arrived in <week. During the pandemic! Great Job Everyone.
 
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