Thanks, Ssyko, for morale boost, and thanks especially, bob bare, for your voice of experience. Being "into physics" in my case (and for many) can mean forgetting to think about things like plain ol' dirt. Had the scientist in me prevailed, I would have attempted separate experiments to separate the variables affecting the problem:
1) Since the nominal-10-KOhm thermistor on my unheated reference side was 11% too high, solder a nominal-100-K thermistor in parallel with the 10K to match the sensors that I presume ought to be matched and were not; and after trying that and (ugh!) removing the corrective 100K component for separately evaluating the following step ...
2) Clean off the sensor probe, in particular the downstream heated green "tongue" (which looked clean to begin with, but the unaided eye can deceive), so that the air flow would remove heat from the dust-free sensor surface with the original efficiency of the new stove.
The frustrated-with-bad-stove engineer in me dispensed with the scientific controls and did both corrections at once, and I cheerfully report that the flow sensor error warning is gone and -- thank you for your wisdom on this, bob -- the flame looks like it's getting the proper proportion of air: not short like a blowtorch and not lazy orange tongues reaching high into the combustion chamber. In the months leading up to the warning beeps and error messages, the flames were getting shorter and more blow-torch-like, a seeming indication that the flow sensor was under-reporting the air flow and the blower control was responding by blowing too much air. The fact that the problem was progressive would point to cumulative sensor dirt buildup, while a system with properly matched temperature sensors would probably take longer to develop significant problems.
So for others frustrated with this problem, refer to my first entry in this thread, find that red rubber body sensor whose photo Ssyko provided, take it out, clean the two green circuit board probes that normally extend across the middle of the air inlet tube, and put the sensor back like you found it. For removal, you'll have to cut the plastic tie wraps securing it (if the factory did yours like they did mine), so obviously you'll need new tie wraps to put it back securely. I cleaned the sensor with a cotton swab dipped in acetone, but 90% isopropyl alcohol (prefer to 70% because the 90% dries better) would probably do just fine. No guarantees, but if the stove worked when new and then developed this sensor problem, there's a good chance the sensor cleaning will fix it (if I'm not putting too much stock in my statistical sample-of-one
).
I was unable to find any advice or instructions like this in the Ravelli manual, and I could not identify the flow sensor in the system schematic on the next-to-last page. To those who service and clean these stoves, I'd guess that pulling out and cleaning the flow sensor should become a regular part of maintenance. And, Ravelli should get the message.
1) Since the nominal-10-KOhm thermistor on my unheated reference side was 11% too high, solder a nominal-100-K thermistor in parallel with the 10K to match the sensors that I presume ought to be matched and were not; and after trying that and (ugh!) removing the corrective 100K component for separately evaluating the following step ...
2) Clean off the sensor probe, in particular the downstream heated green "tongue" (which looked clean to begin with, but the unaided eye can deceive), so that the air flow would remove heat from the dust-free sensor surface with the original efficiency of the new stove.
The frustrated-with-bad-stove engineer in me dispensed with the scientific controls and did both corrections at once, and I cheerfully report that the flow sensor error warning is gone and -- thank you for your wisdom on this, bob -- the flame looks like it's getting the proper proportion of air: not short like a blowtorch and not lazy orange tongues reaching high into the combustion chamber. In the months leading up to the warning beeps and error messages, the flames were getting shorter and more blow-torch-like, a seeming indication that the flow sensor was under-reporting the air flow and the blower control was responding by blowing too much air. The fact that the problem was progressive would point to cumulative sensor dirt buildup, while a system with properly matched temperature sensors would probably take longer to develop significant problems.
So for others frustrated with this problem, refer to my first entry in this thread, find that red rubber body sensor whose photo Ssyko provided, take it out, clean the two green circuit board probes that normally extend across the middle of the air inlet tube, and put the sensor back like you found it. For removal, you'll have to cut the plastic tie wraps securing it (if the factory did yours like they did mine), so obviously you'll need new tie wraps to put it back securely. I cleaned the sensor with a cotton swab dipped in acetone, but 90% isopropyl alcohol (prefer to 70% because the 90% dries better) would probably do just fine. No guarantees, but if the stove worked when new and then developed this sensor problem, there's a good chance the sensor cleaning will fix it (if I'm not putting too much stock in my statistical sample-of-one
).I was unable to find any advice or instructions like this in the Ravelli manual, and I could not identify the flow sensor in the system schematic on the next-to-last page. To those who service and clean these stoves, I'd guess that pulling out and cleaning the flow sensor should become a regular part of maintenance. And, Ravelli should get the message.
