I don't normally mess with fireplaces , but this sweet old lady talked me into taking a look at hers. When you turn it off, the flame dies down for about a second and then a small explosion occurs. It doesn't always do it, but it is kind of scary when it does.
All I know to do is clean the burner (one piece cast rock looking thing) and check the gas pressure. Is there anything else I should be looking for?
primary aeration, manifold pressure, damaged burner, burner ports reamed out too large, LP gas.....
Keep the fire inside the fireplace.
how big of a small explosion? Just a *poof* or does it flex the glass and rattle the front? Knowing more information would also help.
That's called extinction pop. It's usually caused by gas in the burner that's moving too slowly.
If the gas in the burner is moving fast enough, the gas can't burn down inside the burner and must burn on top of the burner where it should. If it's moving too slowly (as it is when the gas is shut off) there is a tendency for the gas to burn down inside the burner tube, causing the extinction pop.
So you probably need to lool for ways to increase the gas flow through the burner a bit --- by checking to make sure you have a properly sized burner orifice, proper manifold gas pressure and a properly adjusted and clean primary air shutter.
This is not generally a hazard ---just an annoyance.
Are you sorry you started working on fireplaces yet? This can happen on other kinds of burners as well.
Thanks for the tips so far.
It is natural gas, I haven't checked manifold pressure, all I've done so far is a visual and told the customer I would research before trying anything. I've been working on gas furnace's for almost ten years now, and I've never seen this before.
The burner is one big piece of cast shaped like a rock with several holes where the gas comes out. It's made by Travis Industries, I couldn't find much more info other than that. She's lived in the house two years, and it just started doing it last year. The newest date I could find is 2001, so I guess it to be 4 or 5 years old.
When it does explode, it does flex the glass a little, definetly not like when I turn my BBQ off and get a little puff or pop.
Any info is greatly appreciated, I'm trying to help this lady out since there is really no one else to call around here. I'm leaning towards pulling the burner and cleaning, followed by checking the manifold pressure. What should I expect for pressure? 3.0 wc?
There was a popular furnace some years ago in my area, Ontario, with a big cast-iron inshot burner, and extinction pop was a fairly common problem on them. Annoying, and it often took quite a bit of time to resolve. In a few cases I recall replacing the valve because they were a slow opening type HW valve that seemed to close a bit slow too, sorta slowing the gas flow to a stop. I doubt that's your problem, but keep it in mind.
Manifold pressure should be on the rating plate, probably 3.5". I'd clean the burner thoroughly, make sure it's properly aligned, not sloping downward, and if there is an adjustable air shutter, try adjusting it. Good luck.
<< Extinction Pop
Defective gas valve
The above website lists replacing the gas valve as tyhe only recommended solution for extinction pop. There are other things I'd try first as I listed in an earlier post, but this if all else fails, replacing the valve would be in order.
This sounds like old equipment. Replacing it with new equipment might be better than putting a new valve in an old fireplace.
Had this the other day on a fireplace. I tried everything you guys all ready mentioned to no avail.
Through trial and error I discovered that the problem was log placement. Apparently the last tech to clean the fireplace replaced the logs improperly. I must have tried 10 different log placements before getting it to work. I still tink it's not quite right but it lights up and shuts down very well now.