Have American Standard gas furnace about 6 years old. The glow ignitor glows and starts the first two tubes on fire but it won't spread upward to the remaining 3 tubes. Since the flame sensor is on the last the tube and the flame doesn't reach it, the gas then shuts off and the furnace goes into shut down. Both the ignitor and gas valve and circuit PCB have been replaced. At first if you banged on the gas tube going to the gas jets it would sometimes spread the flame up to ignite all the tubes. Now the only way to get the furnace on is to manually ignite the tubes oncew the gas valve turns on. ANy ideas would be appreciated. Thanks
Shut the power off to your furnace. Remove the burners completely from the furnace. Use a wire brush and clean them extremly well on the end the flames come out of. You may need to use a knife of some sort or a small tipped flat screw driver to clean the slotted portion. Use compressed air and blow all of the loose debris out of them after you wire brush them. Reinstall the burners and power the furnace back up. Let me know if this does not do the trick, you could have gas pressure problems. Give the burners a try first.
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Thanks for the help. Turns out to be a pressure problem. Have only 20% of the pressure at the out building as I do in the house. The house is about 100 feet from this furnace so must have a blockage or leak in the line. Trying to figure out next steps. Probably pressure test the line.