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

 

I doubt it's a gas pipe obstruction but it could be an undersized line not able to deliver the proper flow in stage 2 mode.

 

Sounds to me like a stuck primary regulator in the combination gas valve. This will require the combination valve be replaced. Cost of the valve is about $100-$200 and then the labor for replacement, maybe an hour or so depending on the installation. In my opinion this should be covered by the manufacturer's warranty.

 

Correct me if I'm wrong.... that could be determined by monitoring the incoming pressure at the valve. There should be a port for that.

 

There MAY be an inlet pressure test port, some valves have them and others don't. IF it has one it will be 1/8 inch pipe thread and most likely the plug has a screwdriver slot. It will most likely be located very near the main inlet to the valve.

This is assuming that the furnace HAS worked properly in the past and all valves between the meter and the furnace are completely open. It also assumes that no additional gas-fired appliances have been added since the furnace was operating correctly.