Pentair MiniMax 400

[Tankless concepts]

hi all,

I need a little help on this one.

Client has in-ground...40K with attached spa.

Here's the story (short version)

I was hired to rewire the pool equpt. area. I did and everything works well. In testing the pool's heater http://www.poolcenter.com/parts_heaters_pentair_minimax_plus_pg1.htm (this unit has top baffle #39 and in/out water ports are on the SAME side as the electronics (opposite the diagram shown)) I noted that when I called for heat (filter running - stat SW to pool - temp dial past current temp) I would hear a clicking and the red service light would come on. I thought of gas......gas was fine. I thought of electronic pilot...confirmed it was working. Did not test hi limits because I had to go.

Fast forward a few days and I am back finishing up a few things. I try the heater again....fires right up and works like a charm. Turned unit off.....than back on 30 min later...works great. I advised the home owner it was oddly working and we'll see how things go. Few days later I am back and tested it again just for SnG's! It's on for a few minutes than off....back on....now I am thinking Hi limit all the way.

Today, I open the control panel and guess what I find? An IID http://www.parts4heating.com/ProductDetails.asp?ProductCode=S8600F that has melted.

So, instantly I think...ohhh, it's bad, order a new one and all is well!!

hmmmm......ok, so I have a degree in electrical engineering, but it's been a while since I did component level work. However I do alright.

Here's the issue I am having:
As you can see from the link, the picture of the IID (mine looked exactly like that) is a simple S8600F Nat gas.

Imagine taking that controller and a heat gun and just go over it over and over again until all the plastic has melted to the contours of the components....that's what I have here.

So just a bit ago I carefully broke away all the hardened brittle plastic to examine the board. I saw not one burnt trace, not one burnt component, no trace of an oder when electronics components fry. It should also be noted that the molex plug and two grounds as well as the 24vt and coil ignighter (thin blue wire) was not really damaged. Damaged in the sense of a shorted wire that is. I saw some slight overheating, but not enough to break the wire jackets or deform any part of the crimp connectors of the molex plug.

So here's where I could use a bit of experience.....

Is flame getting to an area that it is not supposed to and heating up this IId to a point where it melts the casing? Is it possible the internal transformer shorted itself out and that generated the heat to melt the case?

Would it be wise to go back and open up the shell and look for overheating marks on the back side of that front panel?
It should also be noted that the stat controller board appears to be in working condition. I noticed no signs of damage or stress. All the LEDS work, the dial temp pots appear to work, and that tells me the water thermistors are working well too. because a call for heat is happening, but the IID ain't having it.

I hope I gave enough details and your responses are greatly appreciated. BTW, I am a master tankless water heater installer. I train installers on correct methods of installation as well as AHJ's on what to look for on different types of installs....if you need assistance with any of that stuff......happy to trade favors.

Thanks,
James

 

[spishex]

So did the new IID melt as well or are you just trying to figure out what happened to the old one?

Looking at the front panel is a good idea. Often you'll see an obvious scorch trail along the wiring diagrams and other bits of paper that are taped inside.

 

[Tankless concepts]

I just pulled the burnt up IID last night as I was getting ready to leave. I have not ordered a new one yet. I don't want to install a brand new unit, to only have it melt after 20 minutes of use.

What could be causing this?

 

[spishex]

Are you looking at a Minimax Plus or a Minimax NT? The NT will have a digital display. Nevermind, I see you're working with a Minimax Plus from the original post...

Is it mounted near a wall, or even better is it mounted in a corner? If so it's possible that there's enough wind coming down to cause the flame to roll out toward the IID. I'd expect to see some burnt wiring as well, but your other option is electrical from an overcurrent problem, maybe because the ignitor wire is shorting somewhere, and judging from your description of the board that's not happening. If it's in a bad spot for down drafts a vent kit assembly will help, assuming there isn't already one installed.

You may also have some insulation that's missing in that one spot. Maybe something was living in there.

In any event, a problem with the IID should be giving you an ignition problem and not so much a problem with cutting out. That's more likely to be an issue with the pressure switch or hi-limits, OR it could be the thermal fuse has an issue since there was enough heat to damage the IID.

 

[Tankless concepts]

Well, It was bugging me so I went back......it was a good thing.

In looking at the casing sheet metal behing the IId, it was all warped and bent out of shape. I took the top off to get access to the exchanger and it was a mess. All 4 or 5 rows of the exchanger had fallen in the middle, seals around the heating element were breached and all the heat sink fins were totally clogged which is what causes the very high temps internally, but with poor output performance.

Long story short, it is just not worth fixing. So I need a new unit. You know the size I have now.....I like the brand Pentair but am by no means married to it....what is a good reliable heater? It should be noted the way this ones termostat is wired is via 3 wire remote....AKA very simple...nothing fancy these are old folks that like to kee things simple, but maybe I can adapt to it...what say you?