I have a Ruud/Rheem RGRC-06EMAES furnace made in 2011 Oct.When it tried to start up, the ignition sparks could be heard but no flame appeared indicating that the gas valve was not opening. Studying the diagrams, there are many sensors that have to be happy before the gas will come on. It was straightforward to isolate the problem to the “Drain system pressure switch” which would not close. To determine if the problem was with the switch or the “pressure” source, I used tubing from a stethoscope to apply mouth pressure to the switch with an ohmmeter connected. The switch closes when a very slight vacuum is detected, probably “-0.40 PF” as read from the label on the switch.As a unit of pressure, PF is an archaic unit used in agricultural science to measure "soil suction" or soil moisture tension.
See: https://www.unc.edu/~rowlett/units/dictP.html.So this vacuum switch appears to be OK. I blew into the red tube apparently coming from the low point in the heat exchanger
to drain off combustion condensate. I sensed very slight resistance to blowing into this tube. Nevertheless, I must have dislodged something inside the heat exchanger, because the vacuum switch and consequently the furnace have been working for days after doing this.I’m surmising that some kind of crud must be inside the heat exchanger. There are many dead insects (gnats?) on the horizontal surface that separates the upper and lower sections of the furnace. Are these also in the heat exchanger where they might have been seeking water?My prediction is that the furnace is going to shut down again in the same way it recently did. But I have no idea how often this might occur. I want to pursue this, but so far I see no reasonable way to gain access to the interior of the heat exchanger. I thought I might be able to remove the induced draft blower. But some pictures of the heat exchanger show a much smaller hole facing the input to the blower than would be useful. What is the best way to inspect the floor of the heat exchanger, especially near where the condensate drain attaches to it?If I need to clean some crud out, how can I get access to do so?If I have to remove the induced draft blower, where can I buy the black rubber caulk that was used to seal the connection to the exhaust of the blower?
JA: Did you double-check the thermostat's settings? And what about the filters?
Customer: Please read my text before responding!
JA: Do you plan on doing the work yourself?
JA: Anything else we should know to help you best?
Customer: I sent considerable detail in my original question but I can be reached at***@******.*** if you need to ask more.