Water heater popping/knocking sounds caused by dust?

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Davilo

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I have a 9 year old A. O. Smith GVR 40 100 water heater that was making loud knocking/popping sounds whenever the burner was on. I was having to relight the pilot light at about once a week and the burner flame was blue with the edges of the flame rolling off and downward from the burner. The hot water from the sinks and shower were just slightly above luke warm temperature.

Over the months the popping sounds were getting progressivly louder and, assuming that the cause was mineral buildup in the bottom of the tank, I was getting ready to buy a new water heater. As I was preparing to remove the old heater I noticed a plastic air filter attached to the bottom of the heater. I removed and cleaned it (it wasn't very dirty) and vacuumed out the area below the tank via the opening where the filter goes. I also vacuumed out the area where the flue pipe comes out of the top of the water heater.

The result: The heater is no longer making the knocking/popping sounds, the burner flame is orange with no flame "dropout", the pilot light no longer has to be relit and we have hot water again.

What I learned from this is that when you have a water heater that's making popping/knocking sounds you can't automatically assume that the cause is mineral buildup. A little housecleaning may be all that's needed to restore the water heater to working condition.

Can anyone explain to me how a little dust can cause a water heater to mimic the symptoms of mineral buildup in the tank?
 

FullySprinklered

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I replaced a w/h up in Dahlonega a few months ago. The old one was stinking up the house when it cycled on, and it had a big swath of smut on the side from the access door on up. When I cut the old one loose and rolled it out of the way, it took a big chunk of vinyl with it. The flooring had bulged up from the heat, covered the airway under the appliance and stuck there, suffocating the water heater.

I didn't operate the old heater, and don't know if it was making noises or not. As a guess, maybe the flame on yours was sputtering from a lack of air.
 

WorthFlorida

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The popping sound was the flame out. If you ever used a propane torch and turn it off it will make a similar pop sound. Sometimes the outdoor gas grill will also make a pop noise. With enough pressure the gas flame is burning at the nozzle tip. When the gas is turned off the pressure drops and the flame actually travels up the gas tube or pipe because the atmosphere air pressure is now greater. With the right amount (or lack) of oxygen and gas there is a very small explosion occurring at the bottom of the tube and pop goes the weasel.

About your water heater it probably was the pilot light not keeping the thermocouple hot enough, therefore, the gas supply is automatically turned off. When you did get a flame to heat the water the lack of oxygen cause the flame to go out then maybe the pilot light. The bottom line is every thing worked as design and it prevented you from having a gas explosion when it flamed out and lack of oxygen will cause carbon monoxide to enter the area.

I never knew gas water heaters had a filter. It must be something new in the last twenty years so i learned something today.
 

Jadnashua

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Pretty much all newer gas WH these days have a 'feature' that prevents it from igniting any flammable gases that may be in the area. It was mandated to protect us from ourselves since you should not be storing any flammable liquids in the area of a burner, and even if you did, they should not be leaking fumes...but, if they did, the newer WH designs won't ignite them and cause an explosion. Won't do anything about them being ignited by some other ignition source, but not from the WH. Different brands use different means, and some of them have proven to be more susceptible to being messed up from dust and lint clogging them than others.
 

KatyKat

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I have heard that strange sounds coming from radiators may be caused by some air that got inside the heater. You should call a plumber. I had troubles with my old radiators but then changed them for something more convenient and reliable - for trench heaters. They were an awesome idea!
 
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