Gas and Oil Home Heating Furnaces - Furnace problems?

To whom it may concern,

I have a question about my Amana Air command 80 furnace model# GUI070B30B installed in 1991, and I am hoping that you could lead me in the right direction. First the "glow plug" ignitor went out. I replaced this and the furnace functioned fine for about 2 weeks and then the flame rod sensor went out, I know it was this because the burner would ignite and the shut off right away. I replaced the flame sensor and the furnace will run longer, but only for about 5 minutes and then the burner will shut off. The furnace will start up again aand keep cycling like this until it reaches the set point. I even set the setpoit 10 degrees higher to see if it could possibaly be a thermostat problem but it keeps cycling. I trouble shot the furnace and thought that maybe there was a fault with the ignition control module so I replaced the white rogers ignition control with a Honeywell S8910U. But the furnace keeps cycling with the new ignition modual. The fan limit control FL seems to be fine, the limit side is a normally closed switch and it stays closed through the entire cycle. The primary rollout limit ( fancy name for a thermo couple - I think ) starts off when cold at 0 Ohms and reached about 40 Ohms when the furnace shuts off. There is a pressure switch for the combustion blower motor, this seems to be fine the motor runs through the entire cycle. The gas valve I do not know how to properly check but obviosly lets gas out for a little while. The combustion relay and fan relay also function properly.

So I am down to this,
New flame sensor is faulty
Bad ground when system heats up


Any ideas on what the problem might be?

I find this furnace stuff frustrating being I feild repair industrial machines such as CNC's and my home furnace has me confused!?

Any help you could give me would greatly be apreciated.

Thank you and happy holidays,

Best regards
Aaron Reinhart

Aaron,

When you says it runs for 5 minutes then shuts off.. Do you mean the whole system shuts down then starts off again right away? Or it shut down for a few minutes and starts over?

Remove the t-stat from the sub base, and jumper the R and W wire together and see if the system stays on the whole time this wire is together. If it does stay on the whole time. then it may be the stat itself.

If it just stays on for 5 minutes, then there something in the furnace itself.

let us know what you got.

If you check your safties with your meter set on voltage you should see -0- volts while the system is running and if it opens and shuts down the furnace you will see 24 volts across it.

Thank you Jay11J and Mattison for the response. I apologize that I posted this question in the incorrect forum. It was the first time I was to this sight. I jumpered out the Stat and the problem still occurs. The complete system turns on as normal, runs 5 minutes and then the burner shuts off, the blower motor keeps running until the fan switch resets. I will need to go through and check the safteys as suggested. The only safety I know how to check is the fan limit switch, relays and door switch. I am still not sure about the flame sensor and gas valve. Thank you again for the information.

Hello Jay11J and Mattison,

I think I figured it out, I hope? I discovered that the pressure switch is dropping out right when the buner goes out. From the other posts it sounds like the pressure switch is a common failuer? The switch is from 1991. I do not quite understand what makes the pressure switch activite from NC position to the NC postion. I see the hose connection to where the cobustion blower motor is mounted, does this motor make the pressure differance? Being the switch seems to be deactivating the burner because it things it is an overheat ( connected in series with the FL ) I will try replacing the hose and switch. But I would like to understand a liitle more on how it works. Thank you again for your help.

Best regards and happy holidays!

Alot of times you can just blow that hose out. You may also want to check the flue and make sure nothing is in there. That switch just prooves to the system that you've got a good draft.