Pentair Mastertemp 400- No Power, Screen, Lights

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Iskinxs2024

Iskinxs2024

Bronze Supporter
Mar 23, 2024
8
Houston. TX
Pool Size
28000
Surface
Plaster
Chlorine
Liquid Chlorine
I have 12 year old Pentair Mastertemp 400 heater, which has worked great up until now...I tried to turn it on the other day from the panel (Pentair Easytouch Control System) and nothing happened - completely dead. no power, lights, or errors. I search the forums on this website and found some very helpful information. I followed the troubleshooting from this thread - Pentair Mastertemp 400-Blank Screen-No Power which explained my same problem with same hardware. I jumped the fireman's switch and it worked manually which lead me to the wire connecting the switch to the low voltage panel. I performed a continuity test on the wire itself and found the orange wire was cut somewhere. So I replaced the wire. Interestingly enough it was CAT 5E General Cable 4PR 24AWG IWC - standard network cable. I happened to have a CAT 6 4PR 24AWG cable so I used it. After connecting it to the panel and switch I proceeded to turn on the heater. Nothing turned on but i did receive a 128 R=8 code and the screen went blank. I checked the board under the keypad and no error lights. If I press the pool on button it turns on but the service heater light is also on. Why would it work fine manually when the firemans switch was jumped, but not work now...One thing that I was afraid to try is switching the two plugs on the firemans switch. I don't remember which wire was supposed to be on the fuse side and the other. so I guessed. I did take a picture of the low voltage side (attached). Any ideas on why the code when using the panel vs manually pushing the pool on button? Any help would be greatly appreciated.
 

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My MasterTemp shows 128 for a couple of seconds when commanded on by automation. I believe it's normal while the heater is booting up. Then water temperature is displayed. Have you seen this?

Pentair MasterTemp Heaters - Further Reading

www.troublefreepool.com www.troublefreepool.com
 
Welcome to TFP.

If you are getting a "Service Heater" LED, then you will have an error LED on the control board or the Fenwal. Check the Fenwal box LED for blinks.

The fireman’s switch has no polarity.
 
ajw22 said:
Welcome to TFP.

If you are getting a "Service Heater" LED, then you will have an error LED on the control board or the Fenwal. Check the Fenwal box LED for blinks.

The fireman’s switch has no polarity.
Click to expand...
Thanks. I will pay more attention to the control board..
 
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After a little more troubleshooting I think my problem is with the Pentair Easytouch automation. When I select "heater" I do get the 128 and R=8 and then nothing. Usually the fan kicks on (automatically) and then the heater a few seconds later. I can manually select "pool on" and the fan turn on and heater works as it should. So I think my problem lies within the automation. Where do I start the troubleshooting?
 
Iskinxs2024 said:
After a little more troubleshooting I think my problem is with the Pentair Easytouch automation. When I select "heater" I do get the 128 and R=8 and then nothing. Usually the fan kicks on (automatically) and then the heater a few seconds later. I can manually select "pool on" and the fan turn on and heater works as it should. So I think my problem lies within the automation. Where do I start the troubleshooting?
Click to expand...

All the EasyTouch automation does is close a relay that closes the 2-wire firemans switch that tells the MasterTemp to run.

Closing the circuit completes the 24V control circuit in the MasterTemp and powers the heater and display. If you see the normal boot up of 888, 128 and then rX where X is the software revision number then the EasyTouch has told the heater to run and the heater has turned on. After that it is the MasterTemp controls to fire the burner and generate the heat.

If the blower fan is not starting then it is a problem with the wiring, AFS, PCB, Fenwal, or fan motor.
 
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Iskinxs2024 said:
Is the Fenwal LED the red light at the top where the arrow points? It’s not on.
Click to expand...
Yes, the LED will flash if the Fenwal has an error.

The F1/F2 contacts on the Fenwal are supposed to close and start the blower motor when you have 24 volts between "TH" and the 24 volt ground. If you have 24 volts at these 2 points and the contacts do not close, you would need to replace the Fenwal.

Check for 24V between TH and ground when the heater starts up.

If you have that then check if there is continuity between F1 and F2 with the wires disconnected. There is just a relay in the Fenwal that connects F1 to F2 when the Fenwal gets 24V on TH.
 
There are some old threads talking about a period when MT's came with an RS-485 interface that was later dropped. Is yours one of those? If so, there are extra ways for things to go wrong.

I'm looking back at your original post. The fact that things work normally if the FS connection is bridged does seem to point to automation or the wiring to/from it. Like either the fireman circuit is closing for only a short time or there's an RS-485 problem.

But I'm just a fellow MT400 owner. Please trust what @ajw22 says.
 
Thank you for your information. I don’t believe I have an RS-485 connection. My unit is from 2007, but how would I know or check? Is something labeled where the wires plug into the automation(easy touch)?
 
Iskinxs2024 said:
Thank you for your information. I don’t believe I have an RS-485 connection. My unit is from 2007, but how would I know or check? Is something labeled where the wires plug into the automation(easy touch)?
Click to expand...

You do not have the RS-485 if you have the 5 button keypad. It was not near a 2007 unit.

You can look on your PCB for the RS-485 connector.
 
ajw22 said:
Yes, the LED will flash if the Fenwal has an error.

The F1/F2 contacts on the Fenwal are supposed to close and start the blower motor when you have 24 volts between "TH" and the 24 volt ground. If you have 24 volts at these 2 points and the contacts do not close, you would need to replace the Fenwal.

Check for 24V between TH and ground when the heater starts up.

If you have that then check if there is continuity between F1 and F2 with the wires disconnected. There is just a relay in the Fenwal that connects F1 to F2 when the Fenwal gets 24V on TH.
Click to expand...

Ok, I set my multi-meter to volts and clipped the probes(pictured). I turned on the heater from the Easytouch and watch the boot up of 888, 128 r=8 and no volts showed. I then unplugged F1/F2 to check for continuity and nothing.
I didn’t know from which end the power is coming so I checked the "TH" wire and the slot on the Fenwal in 2 separate instances.
 

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