Suburban NT-12SE furnace - gas and spark, but no fire - why?
In a previous thread:
http://www.rv.net/forum/index.cfm/fuseaction/thread/tid/26967247.cfm
...I described a problem with our furnace whereby the furnace would only light when the cover is off. The problem continued, but during the summer we weren't using it so it wasn't a priority. That is, until we started smelling gas. We narrowed it down to the furnace, and pulled it out, capping the line in the trailer (and now there is no more smell in the trailer).
We felt the problem was likely the gas control valve, since there's really nothing else to leak aside from the connections, which all checked out fine. So we replaced it.
Now that the furnace was out, we decided to troubleshoot the lighting problem. It tries to light three times and then goes into lockout. There is no flame at any time in the combustion chamber.
Things we have tried:
• Replaced the spark electrode and verified that there is spark in the combustion chamber for the three times the burner tries to light.
• Removed the burner and cleaned all of the openings with a wire brush. Ran a small wire through the burner openings. The inside of the burner appears to be clear.
• Replaced the gas control valve and verified that there is 12 volts DC on the coils when the spark electrode is sparking. The coil voltage lasts for about five seconds for each of the three ignition tries. Measured the coil current and it was approximately 0.6 Adc.
• Removed the gas control valve with the J pipe and gas orifice. Left the coil wires connected. Immersed the gas orifice in a jar of water. There were gas bubbles coming from the orifice for approximately five seconds for each of the three ignition tries.
• Removed the blower cover and verified that the squirrel cage fan was tight on the blower motor shaft. Looked into the combustion chamber and verified that the gas orifice was inserted into the ring at the end of the burner.
• Don’t have any way to measure the gas pressure but tried two different gas regulators one of which is only about two years old.
Does anyone have any idea of why spark, gas and air don’t produce fire?? I mean, it seems simple enough -- have spark, gas, and air -- why do we not have flame? We don't know what else to try and are about to toss the whole thing and replace it, even though they are about $500. We talked with our local RV repair shop, and they don't have any suggestions.
Thanks,
Dave
http://www.rv.net/forum/index.cfm/fuseaction/thread/tid/26967247.cfm
...I described a problem with our furnace whereby the furnace would only light when the cover is off. The problem continued, but during the summer we weren't using it so it wasn't a priority. That is, until we started smelling gas. We narrowed it down to the furnace, and pulled it out, capping the line in the trailer (and now there is no more smell in the trailer).
We felt the problem was likely the gas control valve, since there's really nothing else to leak aside from the connections, which all checked out fine. So we replaced it.
Now that the furnace was out, we decided to troubleshoot the lighting problem. It tries to light three times and then goes into lockout. There is no flame at any time in the combustion chamber.
Things we have tried:
• Replaced the spark electrode and verified that there is spark in the combustion chamber for the three times the burner tries to light.
• Removed the burner and cleaned all of the openings with a wire brush. Ran a small wire through the burner openings. The inside of the burner appears to be clear.
• Replaced the gas control valve and verified that there is 12 volts DC on the coils when the spark electrode is sparking. The coil voltage lasts for about five seconds for each of the three ignition tries. Measured the coil current and it was approximately 0.6 Adc.
• Removed the gas control valve with the J pipe and gas orifice. Left the coil wires connected. Immersed the gas orifice in a jar of water. There were gas bubbles coming from the orifice for approximately five seconds for each of the three ignition tries.
• Removed the blower cover and verified that the squirrel cage fan was tight on the blower motor shaft. Looked into the combustion chamber and verified that the gas orifice was inserted into the ring at the end of the burner.
• Don’t have any way to measure the gas pressure but tried two different gas regulators one of which is only about two years old.
Does anyone have any idea of why spark, gas and air don’t produce fire?? I mean, it seems simple enough -- have spark, gas, and air -- why do we not have flame? We don't know what else to try and are about to toss the whole thing and replace it, even though they are about $500. We talked with our local RV repair shop, and they don't have any suggestions.
Thanks,
Dave
