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Munchkin 140m F14: blower and/or circulation problem?

ErikVErikV Member Posts: 34
2200 sq ft residence, converted gravity with cast iron radiators plus second RFH zone, Munchkin 140M mod/con is about 7 years old with 925 control panel and Vision (outdoor reset) control.

Boiler has begun throwing intermittent F14 codes, like once every day or two. F14 is a fan speed error, "blower too fast, more than 130% of expected rate for more than 60 seconds."  I read F14 usually the blower, sometimes the control board. Both are original on this unit.

I am trying to troubleshoot before I spring for a $400 part.  I have checked the blower molex connections, and the blower kicks in as expected when the bottom connector is unplugged, so no apparent problems there. FYI the blower did suffer from exhaust gas intake for a couple years after the initial install, but I altered the exhaust piping and there is no evidence (new pitting etc) that exhaust gas is still a problem.

Today it threw F14 so I watched it, here is what I saw: Stat calls for boiler and it kicks in, blower purges at high speed, boiler ignites and temp ramps up (system temp is close to set point right now), boiler throttles back to about 1900 (minimum is supposedly set at 1400), 1900 isn't low enough and the boiler short cycles within a few minutes. After this happens a few times, the system throws an F14. If I reset the error, this series happens very reliably right now: a few short cycles, then an F14.

So I put the boiler in test mode, to see if I can get it to run at less than 1900. Minimum I can run in test mode is 1450. But while I am running at 1450 I notice the boiler temp inches way up; after 5 minutes i exit test mode as the system temp is now 180. This thing NEVER runs higher than 160, I think the max set point is like 170 for when it is -20 F outside. I was really surprised, all circulators were humming, and with the volume of water in this system it takes a looooong time to drive up the temp.

SO here's the question(s): could this in fact be a circulator problem, and the blower speed code is incidental due to short cycling? The Grundfos 15-58 FC units *sound* like they are working; should I pull them and test or inspect them somehow? Should I look for a clogged HeatX (ugh)? Or is this more obviously a blower problem to a more experienced eye?

Pics of the boiler are here, post #8 from a couple years ago, but I can post up some more if it would help:


  • Steve WhitbeckSteve Whitbeck Member Posts: 669

    Do You have a strainer in front of the pump pushing water into the boiler??

    If NO then the pump and water tubes inside the boiler are probably full of crud causing the fast increase in temp rise.

    The blower overspeed is a bad blower.

    The exhaust gas reversion will distroy the blower and 925 control.

    Is there at least 18 inches of vertical seperation between the intake and the exhaust pipes?

    The hot moist condensate laden gasses rise out of the blower when the boiler shuts down. The newer boilers run the blower longer to clear the heat exchanger after the burner turns off.

    I update all of the older boilers to the new program.
  • ErikVErikV Member Posts: 34
    Exhaust, crud, blower, 925 board

    Thanks for the reply.

    Three years ago I reconfigured the intake pipe. The pipes exit through the basement wall, so they are a few feet above the ground outside.  I put a 90 degree elbow on the intake and extended it 4 feet horizontal distance from the exhaust. The installer had stupidly (!) put the pipe ends also near a small corner, so the exhaust is still there near the corner, but the intake is a full 4 feet away and out on the open side of the house. Seems this should be sufficient now.

    The short cycling did not happen any more today, once I let the system cool down. So I don't think things are too bad there yet. No more F14's today, even with boiler running most of the afternoon/evening.

    However, I never did go back and install a strainer. Do you think I could learn about the possibility of crud in the water tubes in the boiler, by pulling that pump that pushes water into the boiler, and checking inside it for crud? The pump is isolated by ball valves, so seems it would be easy to pull it.

    Sounds like I may need to get a new blower.

    Is it possible for me to upgrade the 925 board to a longer end of cycle purge? I can NOT find anyone around here who services Munchkins. Or should I get a new 926 board, to protect the new blower? Maybe a blower this year, then a board next year to spread out the cost.
  • Steve WhitbeckSteve Whitbeck Member Posts: 669

    Don't spend the money on a 926 untill you have to.

    If there is crud inside the boiler the damage is done.

    The crud blocks the inlet to the water tubes. This blocks water flow on some tubes and they overheat.

    The HTP rep can reprogram your 925 to the new program.

    I don't know of any other HTP service people besides myself that have the capability to reprogram.

    You need the password to access that feature.

    And I wont give it out.

    You can make any 925 or 926 work on any model.

    I only carry one of each on the truck and program it to the model I need.
  • ErikVErikV Member Posts: 34
    thanks Steve

    Very helpful, thank you for posting up. I'll stick with the 925.  Maybe HTP can point me to a rep this time, a couple years ago the closest was in Minneapolis (3 hours).

    I'm still not clear on this point: is there any way to check for crud inside the boiler?

    And is it still worth it to install a strainer at this point in time? In my other thread where I asked about it, I was not convinced I was getting sound advice - can you mount a wye strainer vertically? I thought it had to be horizontal.
  • Steve WhitbeckSteve Whitbeck Member Posts: 669
    Y Strainer

    It can be installed in any way as long as the flow is correct.

    I would install the strainer now.

    If you remove the pipes connected to the boiler and look into the brass stubs You can see some of the tube openings.
  • JrJr Member Posts: 38
    edited December 2012

    The fan can be tested by making sure we have 120v going to the fan. Then Measure the DC voltage from the red fan wire to the ground while it is connected to the fan. It should be between24-40 volts. If it is lower than 24 volts, check for excessive external loads connected to the boiler sensor terminals.

    Now disconnect the 5 pin plug from the fan and check voltage on the red wire again. If it is now between 24-40 volts, replace the fan. If it is below 24 volts, replace the Control board. 95% of the time it is the combustion motor. Your board can be programmed with the 100 second post purge if you can find a wholesale house that does it.

    As far as your temps creeping up when you were in low fire. you had the unit in service mode which doesnt care what your set point is. You most likely don't have any type of blockage so don't worry. 
  • ErikVErikV Member Posts: 34
    Testing the motor

    Thanks Jr!

    I *think* I get it and will take a look in a couple hours when i get back home. But there are two things about your post that puzzle me:

    (1) I'm not following the statement "check for excessive external loads connected to the boiler sensor terminals." Are you referring to the terminals on the board for the outdoor and indirect sensors? There is nothing on the indirect sensor terminals, and a sensor but no load on the outdoor sensor terminal. I suppose I can check the voltage there anyway, is that the point?

    (2) Even though the F14 intermittent, this test should be informative for blower motor problems?
  • ErikVErikV Member Posts: 34
    Voltage points to fan too

    I have a blower on order that will ship Fri morning. So I checked the voltages tonight, to give me the chance to cancel that order if there was indication the problem is the board rather than the fan. But if I understand correctly, looks like Jr's tests indicate the blower is indeed bad, as suggested.  

    Measurements performed with the fan off, no call for heat.

    (1) Yes, we have 120V AC going to the fan (black wire, 3 pin plug).

    (2) DC voltage from the red fan wire (5 pin plug) to the ground:

        (i) With plug connected to the fan: 37.2 V

        (i) With plug disconnected from the fan (fan kicks in as soon as you disconnect it): 37.5 V

    I checked the DC volts 3 times, same result every time.

    So I interpret the board is always putting out the same DC voltage, as it is supposed to? If so I will let the replacement fan ship and avoid "intermittent F14" becoming "into mittens F14" or worse.
  • JrJr Member Posts: 38
    You got it

    Sounds like you are right on track! Everything you said sounds like a bad blower motor to me
  • Steve WhitbeckSteve Whitbeck Member Posts: 669

    I do it the easy way - I just hook up the lap top and watch the actuall speed as compared to what the 925 control wants the blower to run.
  • ErikVErikV Member Posts: 34
    New fan in, range 175 - 430?

    New blower arrived today, easy install, hopefully this will eliminate the F14 codes. I'll post up if it doesn't.

    The old fan had a lot of corrosion damage. Now that I have re-routed the vent pipes, I will watch carefully the shiny new fan surfaces for signs of corrosion.

    I watched the display readout today for a while, at full burn and then when it was throttled back and condensing. The minimum I saw on the fan was 175, the max is 430. This is different from the range in the manual (140 - 350).

    Does that range of fan speeds (175 - 430) sound normal for a 140m with a 925?
  • Steve WhitbeckSteve Whitbeck Member Posts: 669
    Fan speed

    Erik - Put the boiler in service mode and run the speed up to the fastest it will go and as slow as it will go and see if those #'s match what is in your owners manuall.

    If they do you should be OK. If not then you still have a problem.

    Some models have different RPM's with different years produced.
  • ErikVErikV Member Posts: 34
    fan speed checked

    OK, well in service mode the min is 140 and the max is 430. The manual that came with the boiler does not have specs. But you can find manuals online that say 140 and 350. I'm not going to worry about it.

    It purrs with new new blower, and no F14s at all.
  • Steve WhitbeckSteve Whitbeck Member Posts: 669

    The new manualls and On line does not show the correct RPM's for some of the older boilers.
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