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