Pilot issue?

FanMan said:

I have a new (to me, bought used) Osburn LA30 stove. Most of the time it works great, but twice now I've had a problem:

Normally, when it shuts off I hear the wall thermostat click, the flames stop with maybe a few residual flickers, then there's a final "poof" or "whump" (just like my gas grill) and that's it. Also normally, the pilot is a clean looking blue flame, showing as three distinct jets around the thermopile.

Twice now, however (I only observed it once), when it shut down the flames flickered around for quite a bit longer, and when I went over to watch it, there were weak yellow flames coming out of the pilot. It made the final "whump" late, and then the weak pilot just sort of faded away (not enough heat to the thermopile, presumably, so it shut it down). I was able to relight it immediately and it then looked normal and worked correctly.

This happened right after the gas company filled my propane tank (previously I had drifted a few 20# bottles into the tank myself to check the operation). Can't see how that would affect anything, but I mention it for completeness.

I'm guessing maybe some crud somewhere (this is a new installation, after all) but I'm open to ideas. The fact that it's an intermittent problem and relights immediately is weird, though.

Click to expand...

I'm thinkin that a small amount of air got into your gas line...It may have been a residual from the air that was used to pressurize the new tank prior to shipment. You LP company may have not performed the customary 4 - 5 purges to clear the air...
*Others may chime in at this point*

A couple things happen when a burner shuts down that manufacturers use different valves for.

If a valve is the type that shuts off fully, quickly, the air in motion going into the burner (or up the exhaust in vented models) continues to move for a few seconds. (in unvented - object in motion tends to stay in motion) This air coming out of the burner holes near the pilot creates a "wind" over the pilot to make it waver a few seconds until the air stops completely. This is when a weak or dirty pilot can go out.

Sometimes a two stage gas valve is used to open slowly in stages to start the movement through the combustion chamber an dout the exhaust, as well as the use of slow acting valves during shutting off to prevent pilot wavering or even sucking the pilot out the exhaust by shutting off too quick. (the pilot flame will lift off the pilot burner and almost be wisked away) So many valves will not shut off fully quickly, (dampened valve) and as it shuts off slow, you will see the flames die and chase themselves around the burner until completely off. If this happens too slow, any pocket of gas that doesn't ignite at the burner holes can ignite with the "whump". We call this going out harshly. When this happens near the pilot, it can use up all the available oxygen at that instant, and you will loose the pilot flame due to oxygen depletion. Burner design, pilot placement, LP and barometric pressure, draft, and fake log placement can all effect this.

This is why a pilot can remian lit for days with no problems, and when the main burner is cycled can go out for one of the reasons above.