<style>body{font-family:Helvetica,Arial;font-size:13px}</style><div id="bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px;margin:0px;line-height:auto">There is an excellent video by Technology Connections explaining gas furnaces.</div><div id="bloop_customfont" style="margin:0px"><a href="https://www.youtube.com/watch?v=lBVvnDfW2Xo">https://www.youtube.com/watch?v=lBVvnDfW2Xo</a><br></div><div id="bloop_customfont" style="margin:0px"><br></div><div id="bloop_customfont" style="margin:0px">You can jump to the point about pressure switch here. </div><div id="bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px;margin:0px;line-height:auto"><a href="https://youtu.be/lBVvnDfW2Xo?t=747">https://youtu.be/lBVvnDfW2Xo?t=747</a><br></div><div id="bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px;margin:0px;line-height:auto"><br></div><div id="bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px;margin:0px;line-height:auto">The tubes connect the pressure switches flue, burners, room, etc. The membrane converts the pressure changes in the switch to physical movement. The pressure has a microswitch that is pushed or released by membranes movement. </div><div id="bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px;margin:0px;line-height:auto"><br></div><div id="bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px;margin:0px;line-height:auto">The furnaces validates burnt gases are going out by confirming the exhaust pipe is not blocked (by not having pressure builds up) and that the exhaust fan(inducer) is working because there is a mild vacuum on it's input.</div><div id="bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px;margin:0px;line-height:auto"><br></div><div id="bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px;margin:0px;line-height:auto">All of these parts are really crude and simple. Yes, we could use modern digital systems but the furnaces were largely designed decades ago for robustness and reliably well before modern digital control logic existed.</div> <div id="bloop_sign_1770690643792420864" class="bloop_sign"></div> <br><p class="airmail_on">On February 9, 2026 at 6:32:34\u202fPM, William Park via kwlug-disc (<a href="mailto:kwlug-disc@kwlug.org">kwlug-disc@kwlug.org</a>) wrote:</p> <blockquote type="cite" class="clean_bq"><span><div><div></div><div><br><br>On 2026-02-09 14:54, Mikalai Birukou via kwlug-disc wrote:<br>> <br>>> There are these little pipes that go between enclosed area in furnace<br>>> and membrane switches to detect presence of pressure difference between<br>>> normal/room and that enclosed area with air/fumes flow.<br>>><br>>> Other season, there was a burned ash in one of pipes, after burner, I<br>>> suppose.<br>>><br>>> One more season, I gently blew in and out of pipe into membrane switch<br>>> to hear it flip. It got unstuck, and continued proper operation.<br>>><br>>> This season, a pipe had a drop of water in it. Surface tension in a<br>>> small radius obvious stopped pressure difference from pushing membrane.<br>>><br>>> I guess, cleanup includes dusting furnace, and blowing through some<br>>> pipes. :) Noting that three events happened over 15 years.<br>> <br>> Better word, little tubes, rubbery tubes few millimeters in diameter.<br>> Not pipes.<br><br>Where is this "tube"? What does membrane switch do?<br><br>_______________________________________________<br>kwlug-disc mailing list<br>To unsubscribe, send an email to <a href="mailto:kwlug-disc-leave@kwlug.org">kwlug-disc-leave@kwlug.org</a><br>with the subject "unsubscribe", or email<br><a href="mailto:kwlug-disc-owner@kwlug.org">kwlug-disc-owner@kwlug.org</a> to contact a human being.<br></div></div></span></blockquote>