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Munchkin help needed

ScottSecor Member Posts: 723
A little back-round. We installed and have been servicing about seventy Munchkin boilers since around 2002. Some residential and some light commercial, most of them are used for heat and many of them also provide the energy for indirect dhw tanks. Believe it or not, most of the boilers have given us very few troubles over the years.

Unfortunately, an excellent customer that has us service her boiler every year since installation back in 2009 has a Munchkin T80M that is giving us problems recently. The boiler is locking out on F13 codes. Once about two weeks ago, which we could not reproduce, then again last Friday night. On Saturday morning the boiler control (R2) was reset and the boiler would fire, but F13’d again in twenty minutes of running. The first thing we did was check the wiring harness, closely examine every plug connector (including the pins on the board and the fan motor) and ended up swapping the fan with a used unit from our shop. The boiler fired right up with a relatively smooth light-off. Burner was dialed in with analyzer while the dhw tank and poorly insulated house on slab slowly warmed up. After cycling the burner a few times intentionally my tech thought he noticed the fan spinning very slowly when the burner was no longer firing or in post purge. He left the site late Saturday afternoon and thought the customer would have reliable heat and dhw for the weekend.

Sunday morning, same problem again F13. Told her we’d be back Monday morning. Got back to site this morning, reset control and burner started a little rough. Found fan speed was something like holding 5000 rpm (way too much for light off and too much for max speed on this control). Swapped out the control with a used unit from our stock, for a 140 R2 boiler, knowing it will light off at 2800 and only run up to 3800. Unit fires up, this fan (the 2nd one, which we think is actually from a WM Ultra) still only runs at 5000 rpm. Swapped fan with another identical to fan #2 (probably also from an Ultra) and it would now run correctly (for a 140 control), 2800 rpm light off, 3800 rpm max speed. This would not “make rate” on the high end, but the boiler is slightly oversized. Tech thought it would now run reliably. Speed varies as you’d expect, slow fan for low fire, mid speed for light-off and high speed for high fire. Cycled unit several times, no issues. Fan speed was on the correct every time the burner fired.
4 hours later (this afternoon), the customer calls back and said it F13’d again. Reset control again and fan only spins at maximum rpm, roughly 3800 rpm. Swap control with another R2 control, of unknown BTU and unit behaves the same, with 3800 being the only speed blower will run. tech left house around noon clicking his heels. 5pm, get the dreaded call, same problem.

Just did another internet search and found an old training video from HTP that shows electrical values and much more in-depth measurements. Will perform these tests tomorrow.

As you may have guessed this customer is not wealthy by any means and happens to be a senior citizen that lives alone (I gather she was never married, has no children and is not close with her far away family). I have known her since 1985 and she is the type of person that actually carried every piece of hwbb into the house for us when it started to drizzle years ago. Yes, she is an excellent customer that we want to make happy. Customer trusts us blindly and has the money saved to replace the boiler, or replace the fan with a new one and the control if necessary. I am not willing to replace the boiler unless we have no choice. For me and this tech it’s not about the money (especially on this job), we want to make it right.

Thank you!


  • HomerJSmith
    HomerJSmith Member Posts: 2,266
    edited March 2022
    Is there outdoor reset? What about checking the values of the sensors? Flame look good? Check the grounds. Check the polarity and ground of the electrical receptical. Gas valve and swirl plate look good? Substitute another harness from the blower to the board. I have found that the Molex jacks don't always make good contact with the pins. Substitute the display module.

    Let us know what you find.

  • ScottSecor
    ScottSecor Member Posts: 723
    Thank you, will report back with results.
  • mattmia2
    mattmia2 Member Posts: 8,412
    Is the blower 2 or 3 wire? Is there a tachometer wire to the blower that maybe isn't making a good connection?
  • Can you share the training video with us?

    You've got a new 926 board in there (black transformer)?

    Very unusual. I've never had to dig that deep into a Munchkin. Wish you luck!

    Might be time to replace it, no?
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • ScottSecor
    ScottSecor Member Posts: 723
    Here is the video, tech (my son) is on site right now.
    Alan (California Radiant) Forbes
  • clammy
    clammy Member Posts: 2,983
    Just wondering have you replaced the fan , if I remember correctly if you remove the 5 pin connector the fan should go to max rpm , if not then it is the fan ,if it does go to hi speed then the issue is most likely w the board . I have seen once a issue w the gas valve 3 pin connector which did not adjust the valve correctly and was found after check the voltage between the pins , after replacing the unit ran fine . Also take a look at the manual reset hi limit on the flue outlet I,ve had a issue w one that was getting wet which showed up as a unrelated code ,it’s been a long time since I ve had to dig into one . I know you guys know what your doing but we all miss stuff and no can know it all . Has your tech check the swirl plate and flame sensor readings ? I had to take a look back at your post but at 20 years old I would image that the life cycle of the both the gas valve and blower motor are close to there designed life cycle . A close look at central heat and hot water production run times would help you decide weather to go w new blower and valve or possibly just replace the unit which I know is never in anyone budget . At 20 years old you guys have been doing the right thing I ve seen them last 1/2 as long , my m80 is still running but it’s getting close to replacement but I like being pro active . It sucks w the expense of mod con blower and gas valve s and I see the point of using what u got but there’s always that black hole of it the issue is happening because of a used part or the controller . I know that you guys always do the right thing but hasn’t your tech opened the unit up to ensure that it’s heat exchanger is clean and clear ,a partically clogged heat exchanger May possible throw a f13 code due to a partically clog heat exchanger and the fans inability to reach pre determined fan speed in due time causing the f13 which is if I remember fan speed over 10 % off board speed ? Peace and good luck clammy
    R.A. Calmbacher L.L.C. HVAC
    NJ Master HVAC Lic.
    Mahwah, NJ
    Specializing in steam and hydronic heating
    EBEBRATT-Ed Member Posts: 13,800
    Years ago in the 70s primary controls on commercial burners (we used mostly Fireye "C" series) were basically relays. If you short cycled it from a low water cut off bouncing or a steam control mercury switch bouncing the burner would just shut down and recycle and start up and run.

    When they first started with the solid state "D" series we replaced some of the older controls as they fit the same subbase.

    On certain job we had lockouts. The new "D" series with the solid state electronics couldn't handle the short cycling and would cause the burner to lockout.

    It took us a while to figure this out.

    I had one job with a commercial burner that drove us insane with very random lockouts.

    I sat in the boiler room all morning watching it cycle and finally found the problem.

    A bad door closer on the Men's room door upstairs. Everytime the heavy door slammed shut the mercury in the thermostat (mounted on the wall next to the door) did the dance and short cycled the burner into lockout.

    Spent way too much time on it.

    Those learning experiences are painful
    JUGHNEAlan (California Radiant) Forbes
  • ScottSecor
    ScottSecor Member Posts: 723
    @EBEBRATT-Ed I have similar stories I could also tell (perhaps too many). I actually preferred

    Another saying my old man would use on me and the other employees was, "You are there and I'm not." In other words, your getting paid, figure it out. Most of the employees (including my three brothers) quit soon after Dad uttered these words. I dad's methodology worked for me as I find myself scratching my head and figuring out the 'tricky' ones on a regular basis after more than thirty five years.
    EBEBRATT-Ed Member Posts: 13,800

    Cell phones have somewhat ruined technicians training IMHO. When I started we didn't even have beepers.

    Now, if they can't fix it as soon as they get to the job they call a senior tech, call tech support etc etc.

    Calling someone for "Legit" help is fine BUT did you go as far as you could go before you made the phone call? Have you got out your tools and meters and checked everything you could check and now are legit stuck? And did you gather all the information you could?

    In the old days you stayed until you got it running.

    I understand with the cost of labor you can't have someone on the job wasting time but too many want the easy answer and the quick fix.

    Phones and tablets are good for looking up info though. I used to haul around a truck full of binders.

    The jobs you never forget are like the Munchkin you just fixed
  • mattmia2
    mattmia2 Member Posts: 8,412
    Ultimately figuring out how to fix it yourself without spending an hour on hold takes less time in the long run.
  • ayetchvacker
    ayetchvacker Member Posts: 57
    mattmia2 said:
    Ultimately figuring out how to fix it yourself without spending an hour on hold takes less time in the long run.
    Exactly! Like when I called Honeywell for an issue with a humidifier board and the guy told me to replace the whole humidifier LOL! I told him that was a ridiculous suggestion and he didn’t know what to do haha! What kind of tech support is that???
    Fixer of things 
    Lead Service Technician
    ‘09Moto Guzzi V7