Presently, this furnace relies on combustion air pulled from within a well insulated tight basement. Frequently, the gas burners fail to light despite a normal ignition sequence and a clean HSI. They may light on the 2nd or 3rd attempt, but if they do not, the furnace locks out as expected under those circumstances. Of interest perhaps is that the burners always light if I have the front panel off to observe the ignition sequence.

Could a limited supply of combustion air prevent the gas valve from opening when it should? Also, once they do light, could that same limited supply of combustion air cause the furnace to run rich? The flames have more orange than I would like to see.

If the answer to these questions is YES, it will be a fairly simple improvement to add a 2" PVC direct air intake from outside the home. I may do that anyway.

If I'm way off base on this, then I'll have to investigate further.

  • 1
    Orange/yellow flames bad. You want nice blue flames to see the morning. I would have a gas technician in to check the furnace. Do not guess. Have/get CO alarms.
    – crip659
    Commented Apr 24, 2023 at 19:23
  • Vacuum does not build quickly or intense enough in even a well-sealed basement to cause your problem.
    – isherwood
    Commented Apr 24, 2023 at 19:46

1 Answer 1


I've been fighting ignition problems with 2 K2 (US boilers) boilers for a while now. My tech says that propane burns "dirty". There was a bunch of crap in the combustion chamber, he vacuumed it out, serviced both the igniter and flame detector. They were both failing frequently with a soft lockout which was an "ignition failure". He said of all his customers, people on propane had the worst problems. Oddly enough, he was just here today and serviced them. He also said that propane boilers and furnaces need twice a year service to be reliable. BTW, the combustion air is from the outside. Since you have a "tightly sealed conditioned basement" I'd seriously consider re-routing your combustion air intake to outside. I don't think that getting combustion air from the basement is the root cause of your ignition failures, but getting combustion air from the outside is more energy efficient. Probably your furnace just needs a service/cleaning.

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