Munchkin 140m troubleshooting FO9

CBRob

I've got a finicky munchkin boiler that was getting assorted errors.

replaced the pressure sensor and one thermsistor.

Got a failure to ignite a few times and while troubleshooting it found that I couldn't get the fan speed up.

It would max out 2040 rpms, even when doing a manual override.

It's getting a 20 degree delta even at the slow fan speed.

Electrical test found 119 volts ac power in and 36 volts on the fan control red wire, while connected and while disconnected from the fan.

I've not had a fan speed error, just slow fan speed all the time.

It's a 2002 model year so I suggested it was time for a replacement.

Not sure if a new fan motor or main control panel would fix the low rpm.

Anyone experienced the 2040 max rpm scenario before? I don't think it was slowed down because it reached delta T of 20, the boiler was programmed for a 25 delta T.

Had it running for a while and now back to FO9. I don't think it's the flame rectifier, but some parameter in startup before getting flame sensor signal.

hot_rod

did you try the HTP website? They used to have a very detailed pdf for troubleshooting the controls.

Is it the 925 controller, search for that here at HH there have been many posts on that boiler over the past 15 years.

Molex connectors were a common bugaboo, and an easy first step to check. Adequate grounding was another, remove and retighten all the ground wire bolts.

CBRob

Thanks Bob. You are always so helpful.

I'll look at the website, didn't think there was one since they were supposed to be out of business.

CBRob

Is this the controller number?

CBRob

I think it's an air intake/ exhaust pressure differential issue maybe. The plastic lid doesn't exactly seal tight.

I solved the fo9 error once by removing the flame rectifier during startup and letting a little exhaust blast through the hole. It must run for a minute before it requires a signal from the rectifier.

Alan (California Radiant) Forbes

F09 was a common problem with older Munchkins. Replacing the control board with the upgraded 926 board (part #7250P-731) usually resolves the problem.

I order mine from Jupiter Heating. Once you place the order, email them the model and serial number of the boiler so that they can program the board for your unit.

https://www.jupiterheating.com/htp/parts/7250P-731.html

HomerJSmith

I'll tell you what the problem is. As has been stated it was a problem for many. You know what the fault code is F09 and one can source it in the manual.

This is how you rectify it. The burner tube is secured to the front boiler plate by four screws. These screws loosen after time. The flame rectification grounds thru those four screws. Loose screws = F09 code.

I clean Munchins at 3 year intervals and when I do I tighten those screws really tight. I replace the burner tube gasket if needed. The original gasket was thin and the replacement gasket is much thicker.

So, clean the HX, tighten the screws really tight, and kiss F09 codes goodby. P.S. I clean the two probes with wet & dry sandpaper, too.

Yes, "Molex connectors were a common bugaboo…" I only had one Muchkin where I had to replace a Molex jack. For some reason it just wasn't passing a signal thru to the pin.

The original fan impeller was plastic which failed and the replacement fans have metal impellers.

CBRob

II'll Open it up today and have a look.

Thanks, much appreciated.

Any thoughts on the rpm maxing put at around 2000?

CBRob

I'd say I've got a clogged condensate drip line.

CBRob

Alan (California Radiant) Forbes

Looks like it. I use a compressor to blow back from the end of the drain into the boiler. In most cases, it comes gushing out with all the debris that clogged it. Flush thoroughly afterwards.

HomerJSmith

Ya! you have a condensate drain issue. I would replace the front and rear refractory, do a complete HX cleaning. Remove the refractories before hand. I use CLR cleaner in a squirt bottle and soak it well. Use a stainless steel scouring pad that I get at the Dollar Store to scrub the HX. Use a garden hose to flush the the HX several times until the condesate hose runs freely. I use a feeler gauge to clean between the coils. I also use a stainless wire wheel on a dremel tool and go over the whole HX coils. I bought these wheels at Harbor Freight. Don't use anything but stainless steel to clean the HX. Flush and spray often. It takes me about 3 hours to clean a Munchkin. The longest it took me to clean a Lochinvar was almost 5 hours. Take your time and do it right.

Munchkins need a combustion analysis which is part of my cleaning process.

On low fire the fan rpm is about 1400 and at high fire 3200 as I recall. You have to access the service mode to adjust the rpm up or down. The manual tells you how to access the programing and the code which is 925.

This is what a Munchkin that I cleaned looks like.

Alan (California Radiant) Forbes

On a 23 year old Munchkin, I’d not be inclined to use anything abrasive on the HX as it might be thin and ready to breach.

CBRob

https://forum.heatinghelp.com/discussion/comment/1875744#Comment_1875744

Wow, that is really clean.

Ive got the ceramic pads front and back ordered from jupiter, will get it cleaned up and new gaskets next week.