Hot water heaters should not sound explosive
January 25, 2016 9:39 AM   Subscribe

The pilot light in the water heater has been going out repeatedly. I've since realized that there is a loud bang -- you could even call it a boom -- associated with the pilot going out. Help me either diagnose the problem or come up with a better explanation for the plumber, because his explanation was "Haha ghosts" and "Call us back if it happens again." It happened again.

The original problem started a month ago. The pilot went out and we couldn't get it relit. A plumber replaced the thermocouple and something else. (The burner assembly, maybe? I wasn't there and didn't talk to him.)

The pilot went out again a couple days after the repair. We couldn't get it to relight. A plumber came out and DID get it to relight by turning the gas dial up quite a bit higher than the 'pilot' setting. (It's got an electronic igniter, by the way.)

Later that week, I got up in the morning and the pilot had again gone out.

Sometime after the original repair, I heard a loud bang with a metallic aftertone that I thought came from the neighbor's house. It was loud enough to rattle my wall. I heard it a couple times and wondered what the hell they were up to. One night last week I heard it again and it occurred to me to go out and check the water heater. (I'd gone out and done a sniff test for gas the other times, but didn't remove the cover to see if the pilot was lit.)

Sure enough, after hearing the bang and going out to inspect, the pilot was out. This has now happened three times -- there's been a loud bang, and when I've gone out to check, the pilot was out.

Plumber came out this weekend and looked at me like I was crazy. His argument was that since it works fine once the pilot gets relit, there's nothing wrong with the water heater. Personally, the fact that the water heater is making an explosive sound, and that I can still hear gas flowing after the pilot goes out (and the fact that it shares a wall with my bed), has me freaking out a bit. I'm now turning the water heater off when I leave the house for work because of that gas-continuing-to-flow thing.

The water heater is maybe 5 years old. The bang is not just the whoosh sound of the burner coming on. It's not normal gas water heater popping/gurgling. It's loud enough to be heard/felt in other parts of the house. I don't know if the precedes the pilot light going out, or if it happens after the pilot goes out, but they definitely seem to be associated.

How do I explain this better to the plumber who tried to get me to buy the ghost explanation? He said the next step will be calling the manufacturer. (The warranty at this point looks like it will cover defective parts, but possibly not an entire replacement.)

PS: I know it's not in my head, because the loud bang scares the hell out of my cats.

PPS: Even absent the loud bang, the pilot should not be going out repeatedly. WHY IS HAPPEN?
posted by mudpuppie to Home & Garden (19 answers total)
Get another plumber. There's some issue with either the pilot getting blown out or some other thing.

Having to restart the pilot is not okay.

The bang just plain scares me.
posted by Ruthless Bunny at 9:43 AM on January 25, 2016 [3 favorites]

Sounds like the main control valve is leaky, there's a small gas leak into the main combustion chamber, and once it's leaked enough gas in there to create an explosive mixture then the pilot light ignites it, it explodes, and the explosion blows out the pilot light.
posted by flabdablet at 9:44 AM on January 25, 2016 [8 favorites]

I can still hear gas flowing after the pilot goes out

It's normal for there to be a bit of a delay while the thermocouple cools down enough to shut off the gas. But if you turn it off, and let it all sit until it's cold, and then turn it back on, you should not hear any gas flow until you light the pilot again. If you are hearing it, that might well be the leak that's fuelling your splosions.
posted by flabdablet at 9:48 AM on January 25, 2016

The only thing that can A) bang and B) blow out a pilot light at the same time is a buildup of gas.

I have no experience with these appliances, but combustion is combustion.

On preview, flabdablet's hypothesis sounds good to me; a leak somewhere near the combustion chamber would do it.
posted by Sunburnt at 9:48 AM on January 25, 2016

Call the gas company and describe the symptoms and tell them that you think there's a leak. They will send someone out immediately (last time I had to deal with this, the guy was there within an hour, and that was in response to much less alarming symptoms). The gas company person won't fix your furnace, but they will check for leaks and let you know if this is dangerous (my money is on yes).
posted by firechicago at 10:02 AM on January 25, 2016 [4 favorites]

Could be a problem with pressure variations in the gas supply. Is there a pressure regulator between your heater and the supply?

If it's that, then your plummer is right to say "there's nothing wrong with the water heater", but he's wrong to not say "it's that regulator". DTMFPA
posted by achrise at 10:15 AM on January 25, 2016

Geez Louise..... "haha ghosts"?!? Call another plumber, stat.
posted by easily confused at 10:19 AM on January 25, 2016

It definitely sounds like a combustion sound -- which I told the plumber -- so thanks for helping narrow that. Also helpful to know about the delay in the gas flow stopping as the thermocouple cools.

No pressure regulator between the gas line and the water heater.

This was the third plumber, by the way. We're working with the home warranty company that is failing miserably. (And plumbers who don't want to believe a dumb girl.)
posted by mudpuppie at 10:21 AM on January 25, 2016

I would consider buying a new water heater. Yes, it's an expense, but, GAS...
posted by H21 at 10:23 AM on January 25, 2016

nthing "another plumber."

It's normal for a little puffing/popping sound to occur as the flame catches on the gas, but it should be a little sound you could barely hear. Should be quieter than normal conversation, say..

A bang that rattles the walls? That isn't good. Something's delaying the combustion until way too much gas is getting out there.
posted by randomkeystrike at 11:39 AM on January 25, 2016

Since you have both a pilot light and and an electronic igniter, you won't necessarily see a lit pilot light when you go look at it at a random time, even under normal operation:
Electronic ignition systems

There are two basic types of electronic igniters in modern furnaces: hot surface igniters and intermittent pilots.

Intermittent pilots still use a pilot light, however it isn’t a “standing” pilot light that remains on all the time to ignite the burner whenever the gas turns on. Instead, the pilot light only comes on when it needs to ignite the burner. When the thermostat signals the need for heat, an electric system creates a spark that causes the pilot to come on, and then the pilot activates the burners. When the burners shut off at the end of the heating cycle, the pilot also goes out. This reduces the amount of fuel used because a standing pilot light drains energy.
It would be very nice to know whether the bang comes at the end of the heating cycle after the burner has been on for awhile, or at the beginning.

If at the beginning, I think flabdablet must be right and the main valve is leaking.

But if it's at the end, I could imagine a scenario where your stovepipe is partly blocked or otherwise not flowing well (because of an almost airtight house, for example, which is pretty common these energy-efficient days), and the last bit of gas you can hear flowing after the pilot goes out accumulates in the pipe and then explodes from contact with a burner which is still hot enough to ignite it.
posted by jamjam at 11:41 AM on January 25, 2016 [1 favorite]

(when your pilot light goes out, do you still have hot water?)
posted by andrewcooke at 11:48 AM on January 25, 2016

Call the gas company and describe the symptoms and tell them that you think there's a leak. They will send someone out immediately.

Yes, they take leaks very seriously.* A PG&E engineer showed up 30 minutes after I called them with a "hey, there's a very faint smell of gas around my meter" report, and insisted on also doing a safety check of the heater inside the apartment with a Ghostbuster-ey electronic gas-sniffing gizmo.

(* Maybe qualify this with a "now", because this experience was post-San Bruno; but still, I was impressed.)
posted by We had a deal, Kyle at 12:00 PM on January 25, 2016

I am not any kind of engineer or expert on gas appliances, but my dad and my old coworker are those kinds of people who can fix anything, especially if a book is in front of them. And i've seen this sort of issue before.

I think jamjam is on the right path here with it not being a continuous pilot light. Almost no newer stuff has those.

My immediate guess is that there's either an issue with the vent/chimney not "drawing" properly, or the air intake. This could be the air intake on the boiler, or to the closet its in.

Pretty much i think the pilot is lighting, but too much gas is building up before the main burner lights. I've seen this on everything from barbeques to furnaces, and my oven occasionally does it now that the entire burner enclosure popped some rivets out and is horribly warped.

I would get a different plumber, or even a general purpose company that does all kinds of plumbing related installs(there's several big ones in my city, they advertise on buses, etc) to come out and present this hypothesis. I'd want to verify the vent wasn't clogged on the outside of the house or within the pipe, and that the correct amount of make-up air(which isn't a lot, but is still important!) is getting in to that closet/basement/wherever the thing is.

It could be something as stupid and simple as it doesn't do this if the door to the room its in is left open. In which case... you saw a hole in the door and put a little $20 vent from home depot down near the floor. It could also be half of some kind of critter nest in the pipe. Or a dead rat, or something.

On preview, it's worth noting the furnace at my old place which had ignition issues like this eventually killed itself going kapow like this. Nothing super dramatic, it just destroyed some of its internal sensors and ended up being not worth repairing because other parts were damaged. I'd call a new plumber like, tomorrow morning.

Also on preview, the "turning the gas up higher than the light setting to light" thing REALLY makes me suspicious of it being the intake air thing. It should light at the normal setting unless the air/fuel ratio is fucked up. Which might not be on the air side, but still.
posted by emptythought at 5:16 PM on January 25, 2016

The water heater is in the garage, and it's not a tightly sealed garage. Where does that leave us with airflow issues?

The second plumber, the one who turned the gas up higher to light the thing, told us to check the vent pipe. My ex climbed up on a ladder and proclaimed it clear, but she's also really, really bad at that kind of thing and I should know not to take her word for it. (I actually hope she was right, because I don't need one more thing to be frustrated with her about. I have a bad feeling, though....)

A plumber is coming out tomorrow morning. I'll ask him to check it out. I will also present him with these hypotheses, which put me in a much better place than where I was before. Thanks, people!
posted by mudpuppie at 6:22 PM on January 25, 2016

Once it's fixed, do come back and let us all know what it was!
posted by flabdablet at 8:57 PM on January 25, 2016

Sounds like the main control valve is leaky, there's a small gas leak into the main combustion chamber, and once it's leaked enough gas in there to create an explosive mixture then the pilot light ignites it, it explodes, and the explosion blows out the pilot light.

Ding ding ding. We have a winner.

They're going to replace the control valve, which they hope will solve the problem. The plumber was able to replicate the noise, by the way, by turning up the temp dial real fast. The valve released too much gas and BOOM. I was out there when he did it. Oddly, it sounded less bad in the garage than it did through the wall, but part of that might be the mystery being gone.

Thanks again for the help. I met plumber #4 at the door with your theories, which headed off any postulating about ghosts. :)
posted by mudpuppie at 12:41 PM on January 26, 2016 [6 favorites]

An update, for the record: The problem wasn't actually a faulty control valve, it was delayed ignition. When plumber #1 replaced the thermocouple and burner assembly, he didn't correctly adjust the burner. It apparently was too far away from where it needed to be, so gas was building up before igniting.

Plumber #4 just adjusted the burner and tells me the problem is solved. I want to believe.
posted by mudpuppie at 11:36 AM on February 10, 2016 [1 favorite]

When plumber #1 replaced the thermocouple and burner assembly, he didn't correctly adjust the burner.

No wonder he believes in ghosts. He's probably responsible for making hundreds of them.
posted by flabdablet at 7:32 PM on February 10, 2016

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