Ruud furnace issue
Thanks for the tips, unfortunately cleaning the flame sensor didnt resolve the issue.
This morning, even after cycling the power at the breaker and leaving it off for a while, it immediately starts up with the 3 short flash code now and its not even attempting to light the burners. Yesterday at least it would start OK and shift to the error after 30 seconds or so.
Model number - URKA-A036JK08E
Serial - 1R5539ADAAF359713861
The Draft motor I guess its called does start up, and there is plenty of airflow out of the top of the exhaust on the unit so I dont suspect any clogs there. I pulled the hose off the draft motor assembly and paper clipped it, didnt feel any debris or anything. Reattached everything and still a no go.
However, with the draft motor running I could not feel any vacuum or pressure with my hands, should I? Or is it such a small amount that its not detectable by hand? pulling the hose while the unit is running I can hear a click from the pressure sensor, and then again when I plug it back in. I'm not sure if I should have done that or not, but it seems to indicate that the pressure sensor is doing *something*.
So what next?
OK, so update - Went out with my trusty multi meter and decided to check a few things at the limit switch (its an L125-20f) and across the switch it came up at 0 ohms (well slightly higher but I'll call it 0). Plugged everything up and whamo it fired and has been running OK for the past 15 minutes or so.
It seems as though every time it starts working again (even if briefly) it is after some tinkering with that limit switch. So my questions - what sort of voltage should I see across the wires that goto the limit switch, and what is the normal resistance across the limit switch that I should see? I'm wondering if its a switch issue or a wiring issue.
Last edited by grubbah; 11-20-2011 at 08:44 AM.