MiniMax NT LN 400 blower overheats

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jimshew

Member
Jul 5, 2022
8
Southern California
I know this trash heap isn't going last much longer, but in the interest of learning and for the challenge of it, I just keep kicking it down the road a little further ...

I've replaced every thermistor/hi/lo in-heater bypass valve thing, in the past two years. I'm on the third blower motor in 3 months. it heats for about 20 minutes (surprisingly a good job during those 20ish minutes), then apparently the blower motor overheats and shuts off, staying hot until well after the entire heater (except the blower motor) is ambient temp before it will turn on again. I pointed the exhaust of my shop vac at the blower (side of heater removed) and it makes an epic difference and keeps the thing running nicely. Nicely enough, that even though I'm sure there's scale inside,but no overheating when I use that shopvac as a 2nd blower motor ...

I replaced that motor with another used (all three same model), and maybe my imagination, but it seems better, albeit same behaviour. Is the issue more likely the Fenway ignition module or my shoddy wiring when replacing that motor?

The paper gasket underneath that motor is shredded, is it as simple as finding a better gasket to insulate it from direct heat transfer?

I don't think it's a oversupply of NG, though the dial disc to what appears to be a gas valve looks broken (not "part of" the heater but is on the NG pipe just inside heater housing, original PB put it in?) pipe is so small I figured it's more likely to be under supply than over, but what do I know (no much, at least with this!).

Any tips appreciated, realizing the most obvious one is "that's a lemon of a heater, dump it" but besides that?
 
jimshew said:
I know this trash heap isn't going last much longer, but in the interest of learning and for the challenge of it, I just keep kicking it down the road a little further ...

I've replaced every thermistor/hi/lo in-heater bypass valve thing, in the past two years. I'm on the third blower motor in 3 months. it heats for about 20 minutes (surprisingly a good job during those 20ish minutes), then apparently the blower motor overheats and shuts off, staying hot until well after the entire heater (except the blower motor) is ambient temp before it will turn on again. I pointed the exhaust of my shop vac at the blower (side of heater removed) and it makes an epic difference and keeps the thing running nicely. Nicely enough, that even though I'm sure there's scale inside,but no overheating when I use that shopvac as a 2nd blower motor ...

I replaced that motor with another used (all three same model), and maybe my imagination, but it seems better, albeit same behaviour. Is the issue more likely the Fenway ignition module or my shoddy wiring when replacing that motor?

The paper gasket underneath that motor is shredded, is it as simple as finding a better gasket to insulate it from direct heat transfer?

I don't think it's a oversupply of NG, though the dial disc to what appears to be a gas valve looks broken (not "part of" the heater but is on the NG pipe just inside heater housing, original PB put it in?) pipe is so small I figured it's more likely to be under supply than over, but what do I know (no much, at least with this!).

Any tips appreciated, realizing the most obvious one is "that's a lemon of a heater, dump it" but besides that?
Click to expand...
If this is a natural gas fueled heater, the brass "disc" should not be in the union in the heater. That is for propane use.
 
I'm only a Mastertemp owner, no kind of expert. But wonder if these motors are somehow set up for 120 volts, but getting 240. That would cause overheating and burn-out as you are seeing. Normally there's single 120/240 12-pin selector plug for the whole heater that handles the change-over. Your heater must have the right plug installed, else the electronics would not be working. So the only way the motor would be getting the wrong voltage would be a wiring mistake.
 
edited the title, originally said maxtemp when minimax nt is the right model ...

This sounds does sound like the issue, thanks! ... I did replace the exact blower model and matched the wiring, but since the two replacements (both used condition) seem to be the same, maybe the original blower had something inside disconnected coinciding with proper configuration for 240v. I realize there's a realistic chance that I crimped badly multiple times on installing the new-to-me blowers as well.

The "original" (previous owner Frankenstein'd stuff already, so who knows) blower drum (I assume that's what it's called) is what corroded away to nothing originally, I can put the motor back and transplant new drum to it, will try that after I take another stab at 240v wiring redo.
 
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jimshew said:
YEP! so the yellow wire was connected and shouldn't have been for 240V. this thing is doing amazingly well now. I guess it was disconnected (not capped) and I mistakenly reconnected it. Guess I have an extra blower motor for future. Thanks a ton!
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Glad it helped.

Hey the whole TFP thing runs on donations. Consider kicking in. I always figure every answer would have cost me a service tech visit - $300 minimum where I live. So the modest donation plans they have seem like a no-brainer.

Become a TFP Supporter
 
So a follow up for the sake of future searches: I had a very short lifetime on the flow valve assembly I recently installed, apparently. It turns out the flow valve power element (replaced a year ago) was already corroded in slightly open position--coincidentally with my blower motor swap out initially. I hadn't let myself consider a recent replacement would have been a dud.

Generally, this heater would do the job to bring spa to temp in 45 minutes, but to heat the whole pool (split body), it would overheat and cut out a few times over the course of a few hours. so the clues were that it would stay lit until too hot to touch, that it worked better on colder days, that it seemed to behave better with a second fan pointed at the blower fan as well. After the initial 45 minutes to an hour or so, it would generally be too hot and wouldn't self-ignite again until it had cooled down significantly.
 
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