Pentair Mastertemp 400 Electrical Issues

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R

R.Towner

Member
Apr 26, 2024
24
Ojai, CA 93023, USA
Hello Everyone,

I bought a used Pentair Mastertemp 400 a little over a year ago. It sat on my pool pad all year until I was able to run a gas line to it. Last week I made all final connections and powered the unit on ready to start the swim season. Unfortunately the unit did not power on. The firemans fuse was blown. I replaced it and it immediately blew again. After taking off all the panels and inspecting all wires I found no damage and no loose connections. I did however find something that I can't figure out. The red neutral wire where the main power connection is made is HOT! (backfeeding) The system is set up for 120v with the correct plug in place. Black wire is hot, Red wire is hot, green ground wire is not.

I have a friend who is a pool tech and he said it was a bad transformer. I replaced that yesterday with no change. Anybody out there ever seen this before? I imagine there is a wire that is plugged into the wrong spot somewhere but I can't find it. Any help you might have would be greatly appreciated.
 

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The heater ships from the Factory with the 240 VAC plug installed.

Installing the 120V plug and then connecting the heater to 240V line current will immediately destroy the transformer, control board and ignition control module, and will void warranty.

If you install the 240V plug and connect the heater to 120 VAC line current, the heater will not operate.

Connect the L1 of the power supply to the black wire, the L2 or neutral lead to the red wire, and the ground wire to the green wire.

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Thanks James, The power supply is 120v coming from a circuit in my easytouch panel. I have the 120v connection plug installed. The problem is that the red wire which should be the neutral wire is getting power from somewhere and sending it back to all my common (white) wires in the panel and messing everything up.

Is there something more I have to do other than install the 120v plug to make it 120v ready?
 
I know you said the heater is plugged for 120V. Great. But then you say both power feeds are hot. How are you measuring this? A 120V supply will have one hot and one neutral line, that somewhere upstream is joined to ground.

Measuring 120V on the heater neutral line could mean the heater is on, but the neutral side of the supply is connected to nothing (open circuit, like maybe a defective power cord, plug, or socket). In that case enough 120V from the "hot" side would be circling back through the transformer to give you a 120V reading with respect to ground.

Or you could actually have 240V power. That would blow up the heater as has been mentioned.
 
R.Towner said:
The neutral red wire is reading 120v at the connection point
Click to expand...
Where is the other end of the red wire connected in the EasyTouch? If you have a 120V feed you should have a white wire coming from the panel into the heater. It would also be connected to the neutral bar in the panel, not a relay.
How are you testing voltage. That small sensor only tells you that there is some voltage, not how much nor were it is coming from. You need an actual meter to determine voltage.
If the new transformer hasn't been damaged, remove the 120V plug and install the 240V one, it may solve the problem. It won't hurt anything if you do actually have 120V into the heater. Get a meter or someone who has one and can use it.
 
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The voltage between black and white lines is 120v. I tried the 240v plug and same thing. I even tested the heater on a completely different 120v circuit. The red neutral wire is reading 120 with a multimeter when i disconnect it from the supply (white) line. The guy I bought it from said it was working before he uninstalled it, but that's just his word.
 

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A pool professional did all the wiring for the pool equipment, we just never tested the heater because I had not ran gas yet. Looks like the black wire is coming from the pump relay and the white is tied in with all the common wires going back to my panel at the house.
 
If you have 120 hot black connected to one side of the transformer, that voltage will transfer through the transformer windings to the red wire, so you will measure 120 from red to ground when the red is not connected to the neutral wire and you will get 0 volts from black to red.

When the red is connected to the neutral wire, you should read 0 volts from red to ground and 120 from red to black.




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I do not know why the fuse is immediately blowing.

Maybe pull the main board and the Fenwal board to see if there are any obvious signs of damage.

Maybe something is miswired?

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I do not know why the fuse is immediately blowing.

Maybe pull the main board and the Fenwal board to see if there are any obvious signs of damage.

Maybe something is miswired?
 

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