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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