Fireplace intermittently making noise when turned on

Question

My tenant just moved out and I went to do the walkthrough on the home. My propane fireplace behaves one of two ways at startup:

• Normally: takes 5-10 seconds to start and then works as usual.

• When I turn on the switch, after a few seconds I see a tiny flame in the fireplace. It stays like that for about a minute (no more clicking). After the one minute, the flame gets bigger and the fireplace visually works as usual but makes a really loud "wind" noise.

This "wind noise" only starts when the fireplace is turned on, so it has nothing to do with the chimney or the outside wind. Once the fireplace is on and is making the noise, the noise won't stop until I turn the fireplace off.

I thought for a while that the tenant may have turned off the propane and it could be an issue with the propane pressure, but the boiler is working fine, central heating, stovetop and the fireplace itself apart from the noise.

The issue seems to be a hit or miss: sometimes the fireplace makes the noise, then I turn it off and when I turn it back on it works as usual.

I'm in Texas.

Link to video: https://vimeo.com/777819739

Answer 1

You're getting flashback in the mixing tube. This is dangerous. Your mixing tube, if aluminum, can melt and the fire can spread.

In normal operation, propane shoots through a tiny hole (called a jet) in the end of its supply pipe. The motion of the propane draws air into open ports near the jet by the venturi effect. As propane and air travel down the tube together, they mix thoroughly. At the end of the mixing tube, the air-fuel mixture leaves the burner through many small holes and it is ignited by a spark or a pilot light. When everything is working normally, the speed of the air-fuel mixture passing through the burner's holes is fast enough to keep the flame burning only beyond the burner's holes.

You have some kind of restriction that is creating turbulence or a reduction in air-fuel velocity. As a result, the flame front is passing back through the burner into the mixing tube, and part of your fuel is burning there.

Look for spider webs, insects, mouse nests or other debris inside the mixing tube or blocking the air vents near the jet or at the point where the mixing tube meets the burner. If none are found, unscrew the jet -- looks like a brass hex nut with a tiny hole in it -- and see if there is any debris inside it or in the end of the supply tube.

As @tetsujin points out, there may be local or state regulations governing fuel gas appliances repairs in rental properties. It's your responsibility to know the law and comply with it, so please do before you proceed.