Question about Pentair Minimax NT Heater

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I turned the heater off for 3 weeks and now when I turn it on it displays EO4 and runs cold for 60 seconds then off to EO4. I have removed the ignitor on the right but the part on the left next to the ignitor is unknown to me. We have had the heater for 3 yr with no problems until now.

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If this is a MiniMax NT STD heater, the part on the right on the bottom is not the ignitor, it is the flame sensor. The part on the left with 2 wires is the ignitor. The E04 code is for a fan failure. This means that either the fan is seized, or the air switch is bad, or the air switch tubing is cracked (this is most common)

If you hear the fan is going, then turn off heater and check the air tube connected to the air switch (3" round disk on right side under the square steel enclosure with 2 wires coming off it on the front).
Remove the tube and inspect it to make sure there are no cracks.

If the tubing is good, and the fan works, you need a new air switch.
If you know how to use a multimeter and/or just need more help, you can reach me @

Posted on Jan 07, 2011

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One other possibility -- this happened to me. There were trees near the unit and some leaf and twig debris had manged to work their way down into the fan. Not enough to stop it, but slowed it down and/or impeded the air flow enough to cause the air switch to register insufficient flow and throw an E04 code. Cleaning the debris out fixed the problem.

Posted on Jan 28, 2011


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You don't mention make or model so here is my guess as to how to thinkout the trouble of what ever is in your attic.

For some reason, your heater is mis-firing. Normally, I would expect 3 to 5 such events at which time the heater goes out on safety. The heater knows it is on safety but you don't until it gets cold in your house. When you turn the power off, wait the 30 seconds, turn it back on, the heater no longer knows it is on safety (memory cleared) so it fires. Your heater continues to fire until ? at which time it starts counting again to 3 or some number. At the max mis-fire number - it goes out on safety again ... repeat - turn it off, wait 30 seconds, turn it back on - no memory and so forth.

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The EO4 is listed as a Fan Failure. However, these heaters have a tendency to go EO4 for no apparent reason. It is what I call the "heater hic-cupping". The easiest thing to try first is to reset the heaters computer. To do this, you will open the right hand side door, find the POWER toggle switch and move it to OFF. Then turn off the Circuit Breaker to the heater,shutting down all electrical power to the unit. You will need to wait about 15 to 20 minutes before you do anything else.

After that time, revese the order. Turn on the Circuit Breaker, then the Power Switch on the heater. Try and start the heater. The computer will "reboot" flashing codes like --- or 888, do not worry about those. When the display panel comes back to normal, check what the heater is reading for a water temp and compare that to what the water is actually. Hopefully, they will be right on, or close, together. The heater will try to start 3 times before going into "Lock Out" mode.

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I am not sure if you have gotten this issue corrected, or not, but the first thing I would try to do is to reset the heater computer system. This sometimes corrects and EO4 error code.

What you will do is open the right hand side door and find the POWER toggle switch, turn that off. Then find the CIRCUIT BREAKER for the heater and turn that off as well, then wait about 15 to 20 minutes. After waiting, you will turn the CIRCUIT BREAKER on first, then the heater. Try and start the heater up.

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