Pentair 400 MiniMax Plus - thermal fuses

[Michdawson]

Hi, I'm new here and a novice at fixing my pool equipment. I'm hoping some savvy pool experts can help me in layman's terms:

My Pentair keeps burning thermal fuses. The first time it looked extremely melted, and a technician came to replace the fuse & cleaned all the burners. He mentioned it may be a life issue for the heater itself, which is about 15 years old. After his "fix", the unit was working fine, but now a week later, the fuse isn't working again (however it doesn't look melted at all, I can just bypass to see it's failed).

I've ordered replacement fuses to avoid purchasing a whole new heater. Any suggestions on how to avoid these issues? I have lots of spiders and the unit is outside (with lots of clearance around it). Should I verify certain parts are clean? Am I doomed to buy a new heater just as we leave swimming season?

Thanks in advance!
Michael
Lafayette, CA

 

[Rocco]

I have had this happen on my MiniMax 400 Plus as well, I went through three of them in a short period of time. What I had to do was take off the top metal grill assembly and clean the heat exchanger which should now be exposed. I used a shop vac with a brush attachment.

This is where the air will flow from the bottom of the unit to the top and out. If the heat exchanger gets clogged with soot it can restrict airflow and cause a blow back (the flame will roll out from the bottom of the unit and melt the thermal fuse).
Here is link to an Adobe PDF of the owners manual for the device that shows the parts I was talking about. The top assembly is part #39 and the heat exchanger/baffles are part # 36 on page 36.

https://www.parts4heating.com/v/vspfiles/images/pdfs/MiniMaxPlusPowerMaxIG.pdf

 

[ps0303]

Clogged heat exchanger. Take the top off of the unit and clean it out. I usually remove the burner tray and then with the top off, I use a hose with a nozzle on it to clean out the heat exchanger.

 

[wjr75]

My old Raypak heater I replaced the wax fuse with a solid state circuit breaker fuse. It is about the size of a quater with a little red button to reset. That might not fix the problem but at 18 bucks a wax fuse it worked for me for a few years. Have a new heater which all come with the solid state type fuses. I did also clean out the heat exchanger as mentioned above and seemed to help the issue.

 

[Pool Clown]

Cleaning the soot from your heater is addressing a side effect and not the cause. Now i realize that this heater is over 15 years, and (it) probably took that long to build up enough soot to become a problem.

IF... well, WHEN you purchase a new heater,

I would make sure your installer has checked the gas line to be sure that it is large enough to handle the demand of the new heater AND that there is sufficient air available in the equipment area for the heater.

Cleaning the exchanger (and a stock interest in fuse-able links) may give several more years of service. Im just suggesting that a look at venting and gas pressure while replacing your fuse-able link would not hurt.

 

[DHank]

Clogged heat exchanger. Take the top off of the unit and clean it out. I usually remove the burner tray and then with the top off, I use a hose with a nozzle on it to clean out the heat exchanger.

I have experienced the same problem with thermal fuses burning out and I appreciated seeing this advice. After a fair amount of work, trial and error, etc., I think that I have the problem resolved. I had received the advice to clean the top of the heat exchanger, but this didn't help. When I cleaned the bottom a bit with a brush, a bunch of black carbon rained down, but later the thermal fuse still blew. I tried blowing out the heat exchanger with the hose/nozzle as recommended above and a lot more stuff came out (makes a real mess by the way) and I think that did the trick. To the above advice, I would add that you need to completely expose the heat exchanger by taking off the last sheet metal piece on top of it. Then you can really see what you're doing and avoid hitting the insulation with the nozzle by accident, which is what I did, blowing the stuff all over the heat exchanger and elsewhere. It took quite a bit of time to clean it off of the heat exchanger fins.

Related info: I also cleaned off the burner unit with a small, stainless steel brush. I'm hoping that the build-up on the heat exchanger was the reason that, prior to the thermal fuse blowing, the unit had to be cycled on and off a couple of times to get it working. I'm guessing that cycling helped to get a sufficient air flow prior to more severe clogging of the heat exchanger.

 

[Pool Clown]

Actually, complete removal of the exchanger is the only way to completely clean it. This also keeps all the soot away from the burner tray and, well, everything else below the exchanger. Granted, it is quite a job, so an evaluation of heater is in order to determine if it is worth the work (age of heater), or if a new heater is in order.

 

[ps0303]

On many units you can remove the burner tray and then using a hose with a good hose end nozzle on it, spray from the top down and then from the underneath up.

It's a very messy job but can be done. However, like mentioned earlier, you need to address the issue that caused it. Is there a burner tube that is clogged with something which is most of the times what causes this down here.