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I have a problem with my gas furnace. It is a 3 year old Bryant.

Last Sunday I smelled natural gas and found the smell coming from the PVC furnace exhaust pipe on the side of my house. The gas company responded and said the furnace had to be tweaked. My HVAC contractor came the next day and diagnosed the problem as an abrupt drop of pressure from the gas pipe when the furnace went into its second stage of ignition.

When the furnace comes on it initially produces a steady flame but the pressure drops from a 7.5 at 1st stage start up and dropped below .5 a short time later when the furnace burner goes into its second stage.

A gas company rep came back and tested the meter reporting that the gas meter was delivering a steady 7 pressure reading and that the problem likely lies in the gas pipe from the meter to the furnace in my basement.

Has anybody familiar with gas piping ever heard of a gas pipe obstruction that could cause such a pressure loss.

I am concerned because the furnace will be needed soon and am uncertain as to how to proceed with my HVAC contractor and the gas company blaming each other.

Any suggestions on what is causing this problem or any testing or work needed would be greatly appreciated

  • You mentioned the furnace is 3 years old... how old is the gas piping in your home? I'm not an expert but a blockage seems like a possibility, and if both of the parties are right then the only remaining culprit is the piping. If we were to speculate about who's wrong, I'd guess the furnace has more ways of mysteriously failing than the gas supply to your house. – Shimon Rura Oct 6 '17 at 17:38
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Did your HVAC tech disassemble any of the gas supply piping, specifically directly upstream of the furnace control valve/regulator? Any obstruction caused by debris (and yes, this is very possible) is very likely to be at the small orifice(s) associated with the furnace control valve/regulator than at other areas of the gas piping, which have significantly larger bore.

Built-in gas appliances should have a "drip leg" debris/condensate trap just upstream of the appliance:

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Yes, it's possible that an obstruction is in one part of the piping and not in others, although I'm not sure how it would get there without passing through the meter. Our furnace conked out due to low gas pressure in the main line from the street so the gas company reamed out the line and put in a new PVC sleeve at no cost to us. Our furnace tech suggested we turn on all 6 gas burners in the kitchen next time to help determine if there is a pressure problem.

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