Plumbing – Gas Pilots going out

This is a tough one without being there to see it.... The only thing that I can come up with is that you have a 2 stage or modulating gas valve and that when you have your thermostat set at a constant temperature your furnace is only operating on the 1st stage gas flow, but when you bump the setpoint on your thermostat up to a higher setting then the 2nd stage or higher modulation is called for and therefor a higher gas pressure is admitted to the main burners. This second stage pressure may be set incorrectly (too high) and causing the pilot flame to be pulled away from the thermocouple during the heating cycle which will cause the pilot thermocouple to cool off enough to cause the pilot safety to shut down the main gas valve and pilot burner. One other thing could be that if you do have a 2 stage or modulating gas valve and the main burner is shut off before the gas pressure is stepped down to the first stage then the sudden main burner shut down could cause turbulence and be snuffing out the pilot at the end of the cycle. This shut down could be from numerous things like a high temperature limit or other safety device shutting down the main burner while it is in the higher stage burn.

1. Do not use pipe dope. The secret to making gas tight fittings is to screw in each connection until only one or two threads are showing. Yellow Teflon tape makes this easier, but it is not a requirement. It can take up to 24 hours for the steel pipe to seal up, so do not expect it to immediately be gas tight. A 16 inch (or longer) pipe wrench also makes this easy, but it is still quite a workout.

2. Yes, there will be natural gas in the line. It should be at a pressure of about seven inches of water column (equivalent to 1/50 atmosphere, 0.02 bar, and 0.25 psi). If there is a really long and fat pressurized pipe (50+ feet of 3/4 inch) in the system, opening could release a few cubic inches of gas. But it is going to rapidly dissipate and float away. Natural gas is buoyant; propane sinks and accumulates in low places. Personally, I wouldn't worry about gas in the line. Just opening a nearby window is more than enough. (Of course, I don't smoke either.)

There is no reason for a plumber to lay pipe. This is something anyone can do. Homeowners are, in my experience, more likely to do a better job because the professionals don't have to live with the installation.

As long as you do a good pressure test, you can assure yourself and your loved ones that it was done well.