Mastertemp 400 NG Bad Board?

T Man

Bronze Supporter
Feb 26, 2016
13
NE, Indiana
3 year old pentair master temp 400

heat will not fire, blower does not even turn... heat is set at 89*. membrane is showing water temp 107... easy touch panel temp reading is accurate (thermometer in pool 83*). I even dropped the pool water sensor in ice water to confirm... while the easy touch and my ScreenLogic both read 36*, the membrane panel on heater stayed on 107*.
the membrane LEDs should not even be on because controlling heat through screen logic...
tried bypassing membrane by jumping first two pins on master temp control board, nothing. no lights on heater control panel when buttons on membrane are pushed...

my question is, does this sound like a bad board in the heater?
 

JamesW

TFP Expert
Mar 2, 2011
16,037
Probably a bad temperature sensor.


The temperature displayed on the heater is what it's reading from the heater thermistor. Even though the heater is being remotely controlled, it won't run if the internal temperature sensor reads over 104 degrees Fahrenheit.
 
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T Man

Bronze Supporter
Feb 26, 2016
13
NE, Indiana
Fantastic! if this is the culprit, which it seems, you just saved me serious $$$! thank you! mine is looking a bit worn. New one on the way, I will post an update when replaced.
Thank you!
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T Man

Bronze Supporter
Feb 26, 2016
13
NE, Indiana
Replaced the thermistor today with no luck. now the blower will run for a few minutes then shut down... no ignition. kicks back on then off . when the blower does kick off I get a 1 second or so AFS led on back of board. water temp is set to 104* but showing 105* on membrane LED - so the heat will not fire because it thinks the water is above set temp. actual water temp is 86* thermometer in the pool & easy touch panel. I shut the screen logic completely off to omit that possibility. I am not getting a Service Heater light on membrane. I checked AFS lines are clear as well as the impeller... not sure but the manual is pointing to a bad board. do want to just be throwing parts at it either.

thank you in advance for any help
 

T Man

Bronze Supporter
Feb 26, 2016
13
NE, Indiana
well now I'm really confused. started to shoot video as I clicked the breaker back on. temp on membrane pad is set to 104. LED on membrane reads 99 (actual water temp is 86*) blower comes up for about 1 minute then the boiler fired up it ran for about 2 minutes but shut down, blower still running. temp flickers between 99-100-101 and so on... blower still running boiler fires back up after a minute to so, runs 30-45 seconds then off... minute or so later boiler fires back up. it runs this cycle until the LCD on the pad reads 105* then the boilers stays off but the blower is still running. why is the temp off on the membrane pad and of course why is it kicking on/off cycling before it reaches set temp. btw, the video ended up being way too long to post.
 

T Man

Bronze Supporter
Feb 26, 2016
13
NE, Indiana
no luck with a short video

when I click the heater breaker to on, I get all 5 of the LEDs on the back of board on for 3 seconds - few seconds later the blower kicks on at the same time as blower winding up, I get the AFS LED for 1 second... about 3 min later, the boiler will kick on run a couple minutes then off. blower still running minute to minute and a half... boiler fired for about 2 seconds then off.
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JamesW

TFP Expert
Mar 2, 2011
16,037
Remove the thermal regulator and see if that makes a difference.

While you have the hole open, check for a round disk. The round disk is the internal bypass. It allows excess water flow to bypass the heat exchanger and go from the inlet to the outlet.

 

T Man

Bronze Supporter
Feb 26, 2016
13
NE, Indiana
It certainly did not pass the hot water test. didn't move at all. I will get a new one installed tomorrow. Did not see the internal bypass, not able to get 100% in line with the hole (sand filter in the way). fired it up again without the thermal regulator and it did the same thing, but this time heating led came on on the membrane pad. then it kicked off (30 seconds) as soon as it read 104* which is what the pad is set at. so the heater thinks it's reaching the set temp... I'm confused why the membrane panel is reading the water temp 105*? is it possible the thermistor I replaced this morning is bad? brand new package from pool service company.

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JamesW

TFP Expert
Mar 2, 2011
16,037
One big issue that I see is the tab feeder after the heater.

If the pump is off and the feeder contains tabs, the chlorine from the feeder can get in the heater and cause havoc.

I'm not sure what's going on with the heater. Maybe multiple issues.

Since you replaced the thermistor, the water temperature reading should be accurate.

Maybe the new sensor is bad or the wiring is compromised or the board is bad.

If you have a 10k ohm resistor, you can try connecting it to the wires instead of the thermistor and the water temperature reading should be 77 degrees.

If you have a good multimeter, you can check the resistance of the thermistors and the resistance should match the resistance in a 10k thermistor chart.

 

T Man

Bronze Supporter
Feb 26, 2016
13
NE, Indiana
I'm with you on the tabs... the chlorinator is off, I just use it when we are gone. I run the pump 24/7 1950rpm. Pentair rep told me that was "best" for whatever that's worth.
I will let you know what I find out with the resistor & multimeter. your help is very appreciated! thank you very much