knocking sound on gas water heater?
I have a 50 gallon AO Smith gas water heater on the 3rd floor which is used for supplying hot water to the bathroom on the 3rd floor only. I haven't used it since I moved in to this house in December of last year because no one currently lives on the 3rd floor and the water heater went out right after I moved in, and I haven't gotten around to fixing it until this past week.
It's like 11+ years old, so it's at its expected end of life, and I was considering getting the whole thing replaced (would cost around $2k where I live), but before I did that, I bought a new pilot assembly and installed it and was able to get the pilot to ignite.
I've been running it for the past 15min, and I'm hearing some loud knocking sounds
Based on my readings online, it seems this could be due to sediment build up in the pipes or tank, and I should flush out the tank to solve the issue?
Comments
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If you're prepared to replace it, go for it. Just be ready for a possible small leak to catastrophic blowout of the bottom. Being on the 3rd floor, I highly suggest the new one sits in an overflow pan with automatic cold water shutoff valve. Mad Dog
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50 gals for 1 bathroom?
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Thanks. I think the pan at the bottom is the overflow pan? It's certainly not enough to hold anywhere close to 50 gallons of water though :(.
I'm a bit worried now if draining can end up causing leaks/blowouts. Maybe i should just get it replaced…
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Yeah. I think it might be because of the large Jacuzzi tub. Note I'm a new homeowner and bought this house in December, but that's my guess. Other than the tub, idk why 50 gallons is needed
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It is sediment at the bottom of your tank that is impeding the heat from getting to the water. It rumbles and knocks like a tea-kettle on a gas burner that has a "cake" of lime-scale build-up on the bottom of the tea kettle. You can empty all of the water from it and then do an acid treatment of the scale, flush that out…thoroughly and then refill the tank and off you go. Or… you could replace the unit like many (most?) people do. I have a 35 y. o. unit that I clean every 5 years, as above. I use vinegar in my tea kettle.
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Yeah I was trying to save some money before going with a $2k replacement where I would probably end up using a bradford water heater as opposed to another AO Smith. I heard those are better.
One thing I'm confused about is given the sediment build up is at the bottom of the tank, why is the knocking sound more prominent at the top of the tank? It's probably not obvious from the video, but it is in person. In the manual for this water heater (https://assets.hotwater.com/damroot/Original/10004/GCVT-50%20instruction%20manual.pdf), it also mentioned that "strange sounds" could be "Possible noises due to expansion and contraction of some metal partsduring periods of heat-up and cool-down do not necessarily representharmful or dangerous conditions." I wonder if that could be it as well?
I think it's more likely to be sediment though. I've definitely seen it in my water, especially when I come home after being gone after a couple weeks
I'm just hoping that me trying to save money doesn't end up being something that leads to more costs if the water heater were to blowout and flood my house… I did notice that I have a pipe from the overflow plan to the ground which might be a drain so that might help in that event:
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Thats a lot of weight for the 3rd floor.
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Yeah idk. I didn't design this, and I think the 3rd floor was finished before the previous home owners moved in in the late 90s. This is 1927 tudor. I hope they reinforced the load under the water heater and jacuzzi tub sufficiently…
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Hi, There is a good chance that tank has an aluminum anode. These produce lots of corrosion byproduct, which settles to the bottom and helps cause noise. The only way to know the condition of the tank is to remove and look at the anode. I'd be prepared to replace it with a magnesium rod. It looks like the drain pan is actually hooked up to a drain line, which is good 😺
Yours, Larry
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I understand your situation.
- My father installed a 120 Gallon whirlpool tub and tried to fill it with the existing 80 gallon electric water heater only to find out that wasn't gonna work. We did a 40 gallon Buderus indirect off of a Buderus Boiler and was able to fill that tub with no problem with the recovery rate of the larger boiler.
- I replaced a 50 gallon gas water heater for my nephew who had a second floor condo in Ocean City NJ. I was concerned about the existing 2" pan under the tank. I had a custom built 6" pan with a 1" PVC port at the bottom that would feed directly outside I figured if the leak was large enough to fill the pan 4", that a 1" drain could handle the flow until someone noticed the water flowing down the side of the building and address the problem
You have both issues with needing a hot water source that has the capacity to fill the tub and you want it on the third floor. I might suggest that you look into a tankless water that will hang on the wall and have less weight up there. You can also use a switch that monitors for leaks and closes off the cold water supply in the event of a problem. That way a smaller pan under the water heater would be enough.
If you still go with a large tank, then I would suggest a custom built 6” tall drain pan and place the water heater on 4” legs in the pan. Use a 1” Drain connection at the bottom of the pan and run the drain line to an obvious location so you will see the dripping water before it becomes a catastrophe. I have actually placed a secondary overflow drain in the ceiling of a bathroom, just over the shower or tub. It is not supposed to leak but if it ever does, that will leak in a place designed to collect water and will be easily seen by users of that bathroom.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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It does have an anode according to but I don't know the material. I can see if I can figure out what it is. I think I'm going to let the water heater run for a few hours and see what happens. Yesterday, I left it on for 30min and turned it off because I wasn't sure if it was a good idea to keep it on with the knocking sound for a prolonged period of time.
I went to a local hardware store and someone said it could also be due to condensation since the tank has been off for such a long time and that the orange flame is indicative of that as it should be blue had it been continuously running
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If I designed this bathroom, I don't think we would ever have installed the Jacuzzi tub simply because we'd probably never use it, but yeah this is just what I have now.
I will look into the tankless water option. I don't know how long the water heater and bath tub have been up there but I think it's got to be at least 26+ years, and I feel like if the weight caused issues, it would have already caused it?
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Hi, A quick test for sediment and the cause of the sound is to stand by the heater while it's firing and have someone run hot water. This lowers the water pressure slightly in the tank and encourages the boiling noise. As soon as the tap is closed, the heater quiets down. Try it and see what happens. 🤠
Also, if your tank has a hex head anode, you can tell what metal it is by looking at that hex head. If there is a weld bump in the middle of it, it's magnesium. If it's flat, it's aluminum … in your brand of tank.
Yours, Larry
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Hey guys. I turned it back on on Saturday, and on the lower of the 3 heat settings and heard the knocks for a couple minutes but it's been gone and operating fine since then.
At the same time, I did pop up the T&P valve and it started dripping water nonstop. I saw someone oneline mention it could be due to sediment stuck in the T&P valve and they recommended dislodging the sediment by hitting the valve with a hammer (gently presumably) and I did just that and it stopped the leak.
I'm not expecting this to work for a long time but hopefully it works long enough for me to save for a brand new replacement — i'll probably go with a bradford this time.
The hot water looks pretty cloudly, which from searching online appears to be due to air bubbles.
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Hi, Cloudy with bubbles could be a clue. As the tank has been unused for some days, good chance that was hydrogen gas generated by the anode. This would be great info as it means your tank has a working anode, protecting the tank, and the tank is sound. It's not so hard to fix the old tank if you know it isn't about to fail. 😃
Yours, Larry
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