We have a Munchkin condensing boiler configured for natural gas that, with routine maintenance, ran reliably for three years. One morning, it stopped heating, and the controller display showed a code of F13.
The code on the display meant that the blower in this boiler wasn't spinning fast enough to safely open the gas valve and begin ignition. The problem was that, according to the diagnostics display on the controller, it actually was spinning at least 200RPM faster than the lowest speed for ignition. If I reset the controller, it would begin ignition, heat the water, satisfy the demand, and then shut down with that mysterious error code again. Sometimes, it would inexplicably shut down before demand was met.
I decided that I needed to make sure all the sensors were working as they should. One by one, I tested them to make sure the controller responded appropriately. The controller reacted pretty much as I would have expected. While doing this, I noticed that many key parts weren't made by Munchkin. The blower was made by EBM Pabst of Germany; the gas solenoid was made by Dungs of Denmark; the controller was made by S.I.T. Controls of Italy; the rest was apparently assembled in the US. This thing reminded me of the Tower of Babel story in the Bible.
EBM Pabst has a website with lots of data about its blowers. I had presumed that the blower was under some sort of control because, when I unplugged it while powered up, it went to full speed. From EBM Pabst, I found out that if I grounded the PWM speed control line, it should stop and go to a standby mode. I tried that, and the blower didn't shut down. Now I had reason to spend hundreds on a new blower. After replacing the blower and checking for leaks, I put it to the test. Everything worked properly again.
Looking back, I have to wonder whether the folks at S.I.T. Controls considered this failure mode. The F13 code was being triggered because the blower speed was free-running, not because it was under-speed, as the error code documentation suggested. The controller also wasn't consistent about why or how it tripped, leaving everyone wondering what the controller was balking at.
I give EBM Pabst low marks for quality control. S.I.T. Controls gets failing marks for erratic firmware behavior, and poor Internet presence, besides. However, Munchkin completely flunked because of its manual.
Despite detailed performance data, the boiler manuals did not have a Control Narrative section. The Control Narrative explains in gory detail exactly what the automation does in response to all stimuli in every automation state that it could have. It is a key deliverable to clients. As a registered controls engineer myself, I wouldn't dream of designing a potentially dangerous device such as a gas boiler without explicit documentation of this sort.
Without that narrative, even experienced, reputable service firms have little idea what the unit is supposed to be doing, why an error code might be there, or what tests one might use to diagnose it. It is not enough to failsafe on devices like this. Customers or their designated repair firms deserve a reasonable explanation of what kept a device from working.
This entry was submitted by Jacob Brodsky and edited by Rob Spiegel.
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Good job figuring this out. To echo another's post, did you do a post mortem on the blower?
When replacing expensive components at home, I always try to fix the old one to keep as a spare to avoid future expense (takes a little extra time, not always successful, but I usually learn something about the equipment I'm maintaining).
As to the tower of babel, remember that this is a global economy. People usually buy strictly on price, globally. This include's "primes" like the boiler nameplate. It's hard for a company to justify the cost of fully understanding all the features of each component, or of writing a well designed troubleshooting guide. If the product outlasts the warantee period, they have an adequate design. Sad, but it's the state of the times (and of the technology).
I really wanted to do a post mortem on the blower, but it was assembled in a way that made removal of the control board very difficult.
To make a long story short, the motor control circuit board actually penetrates inside the motor. The screws holding this circuit board to the motor were obscured by the impeller casing and casing was not possible to remove until the impeller was removed. The impeller was press-fit using components that I did not have the tools to remove.
My best guess is that one or more of the power devices in the H-Bridge shorted out. This might cause the motor to be less controllable, without actually failing.
As an aside, I would like to note that the world's market for power devices has always been fraught with cheap imitations that are not as robust. In earlier days I used to find fake 2N3055-type bipolar power transistors in failed power supplies. From what I've read in various electronics magazines, these bogus devices continue to find their way in to too many distribution channels.
This goes to show just how difficult it can be to build a reliable product. And where profit margins are very narrow, most people simply do not want to be bothered with this level of diligence.
I would have to agree with you Curmudgeon. The only way that such diagrams would be included is by regulation.
I also have to say that there were parts of this Munchkin manual that had to have been written with an attorney breathing down the neck of the technical writer. The first chapters of the installation manual were so littered with bold face large type warnings of dire consequences that it made reading the rest of the manual far more difficult than it had to be.
This is what I call the "Step Ladder Warning Disease." If you plaster too many cautions, warnings, and bold faced admonitions in a manual, few will read it and most of the public will continue to do the stupid things outlined in the warnings. Frankly, I have seen pilot operation handbooks (for aircraft), and even firearm manuals with fewer warnings than this monstrosity.
The solution is to undestand that this is indeed a gas boiler. Yes, natural gas can be explosive. There is also heat and condensate involved here. If an installer didn't know that, it is very unlikely a bold faced warning will teach them anything.
Attorneys need to understand that writing a manual that people will actually read and comprehend is an art form. The more they inject liability disclaimers in to the manual, the less likely it will be that anyone will be motivated to read the silly thing.
Some day I would like to see a conference between technical writers, engineers, and attorneys on how to build a better manual, because the state of the art right now isn't serving anyone well.
Papst had a name for producing quality stuff so to read of your bad experience is disappointing.
I recently removed two Papst fans from a junked UPS. They had been working for years but still ran smooth as silk. You can't say that about the average PC fan....
Papst also produced an outer-rotor motor which was used in some high-end tape recorders. Weird things, the outer case turned and the spindle stayed still and was attached to a mounting plate.
The error code was confusing. The blower appeared to be under some sort of control because when I unplugged the control lines it went to full speed (as it was supposed to). The service technicians wanted to replace both the controller at the blower to the tune of close to $1k. They lacked any diagnostics to isolate which was broken.
The bottom line: was it not working because the controller was defective, a sensor was defective, or the blower was defective? I do not like to replace parts without knowing with some certainty that it was actually defective.
Yes, I know, from a labor and overall cost perspective, given the lack of information on what the embedded system was supposed to do, their approach is cheaper.
I wonder how many times we have inadvertently installed fake parts into our systems. It is embarrassing to find a good design failing for no good reason. We suspect many things- circuit boards, wiring, etc. without thinking that little IC or transistor could actually have been defective to begin with. Unnerving, at least.
As an OLD Motorola alumnus, I'm exceptionally familar with the "M" seires parts. There's a legit reason for this: these parts have their own proprietary specs, and are SELECTIONS from the parent product line. The spec differences are (usually) narrow range of beta, and (often) leakage current, noise figure, etc. The "generic' replacement part (like NTE) will mostly work, but design margins may be violated and therefore performance degraded. In my 13 "batwing" years I probably set up several dozen of these P/Ns myself. So of course if you characterize a specific M9706, it will fit all the parameters of the MPSA64; however, the reverse is NOT true for other MPSA64s! Given your comment on "proprietary unit" I'm surprised that you didn't recognize that those "M" parts were too!
There is another side to this story that has not been brought up. I've worked in various industries for OEM suppliers and been on numerous system integration teams. For at least the past decade I've seen far too many OEM customers go with suppliers who had never worked on any component like that required for the system, and who subsequently screwed up the programs so severely that they had to be delayed (to the point of missing market windows in some cases!) or cancelled. The reason for the bad sourcing decision? Low bidder, without regard for qualifications! Perhaps DN needs a new blog series called "Managed by Morons."
That is far too often the case. There have been a number of threads recently about component substitutions causing failures. I also blame high turnaround. It seems that three years has become the normal tenure, instead of working until retirement. It seems that as soon as a product is out the door, that the product's designers, and all of their knowledge, are out the door too. The next thing you know Purchasing starts to complain about the sourcing on a component, and Senior Management pressures Engineering to accommodate the change without the time (read as cost) required to fully understand the change.
I worked for one organization that allowed Manufacturing Engineering to specify changes on a design without the approval of Product Development. Worse yet, Manufacturing Engineering didn't even have a EE on staff, so they just followed the recommendations of Purchasing. Purchasing even routed contested ECNs during lunch if one of the primary signatures was against their change. I know it sounds like the premise for a sitcom, but they actually made medical devices.
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