Choctaw H140 pulsating

[heritageequipment]

Hello,

I have a Choctaw H140 that has been heating my garage for about 8 years. The unit is located inside and the exhaust is piped through the wall with about 10 feet of exhaust pipe. It worked fine for the first 5 years, but for the last three is has been driving me nuts. Its current problem is that when cold, it will not start firing with the 10 foot flexible duct attached. If you turn the unit on with the duct attached the unit trys to ignite for a few seconds then the flame out occurs. So to get it to work I have to disconnect the duct, turn it on and let if warm up for about 30 seconds then reattach the duct while the unit is blowing air in my face. The unit will remain working for 20 minutes to an hour then it will flame out again.

When the unit is cold, the ignition pulsates noticeably and it appears that without the duct attached it can overcome this pulsating after 20 seconds or so but if the duct is attached it can not overcome the pulsating and it flames out. There is some issue with airflow and pressure, especially when cold, that is causing it to either barely ignite or not ignite at all. Or maybe there is not enough fuel spray?

At one point two years ago I noticed the arc was no longer existent so I replaced the coil and that fixed that issue. While I had it all apart I inspected everything and even changed the nozzle and everything looks really good and clean. I also bypassed the air pressure switch in the cabinet for testing purposes but that has no effect on pulsating and flame out issue.

Would anybody know where else to look?

thanks

 

[Guyfang]

Pulsating is normally fuel related. Lack of good pressure, or dirt/crap in the system someplace.

 

[heritageequipment]

Pulsating is normally fuel related. Lack of good pressure, or dirt/crap in the system someplace.

Thank you for the insight. I just replaced the fuel filter and it had no effect on the issue. The fuel pressure seems pretty rock solid at 120PSI which is in spec according to the TM, so I dont really know where else to look. I might just throw another nozzle in it, but otherwise do you have any method for diagnosing the issue? It only pulsates when cold for about 20 seconds, then it seems to fire fine.....until the flame out occurs 20 minutes to 2 hours later.

 

[Guyfang]

The fuel tank. Is it clean? There has been times when I saw this kind of problem, and it was something in the fuel tank. The fuel pickup tube would be stopped up after a time, and it was never the same amount of time, and the heater would stop. The blockage would fall off the pickup tube and float around, until we started it again.

 

[Mullaney]

The fuel tank. Is it clean? There has been times when I saw this kind of problem, and it was something in the fuel tank. The fuel pickup tube would be stopped up after a time, and it was never the same amount of time, and the heater would stop. The blockage would fall off the pickup tube and float around, until we started it again.

.
A lot like a ping pong ball in a fuel tank...
Not really because most pickup tubes are filtered with a "sock"

But these heaters... No so much. Trash on the bottom of the pickup tube and it is over like @Guyfang mentioned.