I have a Trane XR90 (natural gas) that was installed in 2005 and has had just basic maintenance over the last 8 years (clean the main blower, change air filters, visual inspection of the clear vinyl drain/condensate tubes). In February 2013 the XR90 started to experience intermittent operation of the burner cycle similar to that reported by many posters on this forum: 1) the thermostat calls for heat, the inducer fan comes on and runs for about 30 seconds; 2) the igniter glows and the gas turns on, the burners light and fire for about 30 - 45 seconds before the main air blower kicks on; 3) a few seconds after the main blower turn on, the inducer fan starts to operate intermittently or kicks out completely, the burners go out and the main blower continues to run for about a minute or two and then shuts off; 4) after a couple minutes later the burner cycle starts all over again.
After reading the postings on this forum I began to check the obvious items: clear intake/ exhaust pipes, clear condensate lines and proper operation of the igniter and gas burners. I then thought that it could be a malfunctioning part such as a pressure switch or worn sleeve bearings in the inducer fan. As I more closely inspected the inducer fan I began to hear a very slight “gurgling sound” after the fan had been running for about 2 minutes. I checked the 90-degree off-white-color rubber drain elbow that drains the bottom of the inducer fan into a clear drain tube and found some debris stuck in the elbow. The debris in this drain elbow accumulated over 8 years and was enough to cause a partial blockage so that the inducer fan would build up a slight amount of water as it was running. As the inducer fan was continuing to run over a few minutes, the amount of water in the fan built-up to the point where it was not able to create enough negative pressure in the burner box which then tripped out the pressure switch and shut down the burner cycle; when the burner cycle shut down completely for a few minutes, the water slowly drained from the inducer fan and the burner cycle would then re-start with the same intermittent operation of the fan.
I removed and cleaned the rubber drain elbow from the fan and also cleaned the inside of the clear plastic drain line with a pipe cleaner from my local craft store. I also removed and cleaned out the white-plastic drain box the connects the burner condensate line and inducer fan drain line to the main drain line from the XR90; this white-plastic drain box was loaded with gunk that accumulated over 8 years of operation and may have also contributed indirectly to the problem. After cleaning out all of these drain line components, my XR90 is now running very reliably with no intermittent shut-downs.
Congrats on your D.Y.I. troubleshooting and repair. I once had a similar problem with the hose between the inducer and pressure switch. Re routed the hose to eliminate a dip which collected condensate and solved it.
Power vent water heater required the pipe cleaner trick to put it back on line.
Good job!
Cleaning and inspecting the trap and drain system is part of the annual maintenance which will help provide reliabole furnace operation.
Cleaning the flame sensor is another task that should be done annually to help insure reliable ioperation.
Tags: troubleshooting, intermittent, operation, trane, xr90, furnace, burner cycle, drain line, main blower, drain elbow, pressure switch, about seconds
