Bryant Plus 90 won't stay running
Asked Oct 29, 2010, 01:30 PM
I have a Bryant Plus 90, model 398AAW036080. Year on rating plate is 1982, but I know it was installed a few years after that since I've only lived here since 1984. I had to have the gas valve replaced in June of 1998. I suspect it is bad again, as here are the unusual symptoms, which lead me to believe that something else is wrong too maybe?;
House is 60 degrees... I turn the thermostat up to 70 (electronic Honeywell Chronotherm III with new batteries in it).
Small blower on the furnace turns on, then about 2 minutes later, the below cycle starts;
---- pilot flame comes on, but stays on for only 10 to 40 seconds before it goes out. It stays off for about 45 seconds before it comes on again. This happened 7 times on the most recent attempt, with that â€śon cycleâ€ť varying from 10-40 seconds each time... it is never a consistent time delay!
On the 8th cycle, after 10 seconds, a loud click came from the gas valve (I believe that is the solenoid for the burner gas?). About 10 seconds later the burners light and then, after a short delay of maybe a minute, the large furnace blower motor starts. But the burners only stay lit for about 7-8 minutes and then they go out (and the pilot flame also is out), even though the house is still cold and the thermostat is calling for heat. Then, after about 2 minutes, the large blower stops, but the little blower stays on indefinitely if I don't do anything else. Neither flame will attempt to light without turning the furnace on and then off again.
If I leave power off for about 2 minutes and turn it back on, then I can get the same cycle to happen again, but sometimes the burners light after one cycle, but the most recent attempt was seven cycles.
I suspect it is the gas valve, but why does the furnace then only run for 7 minutes once the burners finally do ignite? Is something overheating, causing it to shut down? Or is the valve good, but the mail circuit board not sending a signal to the valve to open the valve for the main burner gas? Hate to buy one part, only to find out it is the other. The main circuit board has never been replaced, but the relay on there looks like it's contacts are pretty well deteriorated!
Any ideas would be appreciated. (I have a 2-year electronics degree, in case you are wondering).