How to add a fluid to an A.O.Smith ProMax gas water heater

[Don_S]

Hello all! New member here with the first post. I am just a DIYer and not a plumber!

I have a problem with limescale build up in the pipes in my house. I would like to de-scale the pipes (at least partially) by using vinegar. The procedure calls for adding 2 gallons of vinegar to the hot water heater, and I am not sure how to go about it. Looking at the top of the water heater (An AO Smith Promax gas heater), I see a circular plastic cap which seems to be the only potential place to pour the vinegar into the water heater. The other openings are the cold water inlet, the hot water outlet, the anode rod securing nut and the blower assembly, none of which are accessible to pour fluid into the heater. My question is, what is the round plastic cap covering, and can I safely pry it out to pour the vinegar in? I have attached photos to show the cap in question.

Thanks in advance for your responses!

 

[Twowaxhack]

drain the heater and use a hose and funnel to pour it in through the drain valve at the bottom.

 

[Don_S]

Thanks for the quick reply. That's probably what I will end up doing, but just out of curiosity, what IS that plastic cap at the top? Also, the article I read regarding de-scaling said to pour the vinegar in from the top of the heater. This would be preferable to me since it would only involve draining a couple of gallons of water from the heater and not the entire contents of the heater.

 

[Twowaxhack]

Pull it out and see. Might be just where they pumped it full of foam.

im not sure. You say it’s not the anode.

 

[Don_S]

No, the anode rod opening is to the left of, and partially under the blower assembly and has a large hex nut attaching it to the top of the heater.

 

[Twowaxhack]

Get a pump and bucket. Turn off water to water heater

open a hot faucet

connect pump hose to open drain valve and pump it in from the bottom.

 

[Don_S]

That sounds like a plan! Thank you!

 

[Don_S]

Get a pump and bucket. Turn off water to water heater

open a hot faucet

connect pump hose to open drain valve and pump it in from the bottom.

This brings up another question, however. Will a simple fluid-transfer pump like the one shown below work? (I would have to find an adapter to go from the end of the clear vinyl tubing to the drain valve of the heater). Not sure if this pump can handle the back pressure from the water heater when the drain valve at the bottom of the heater is opened.

 

[Twowaxhack]

I have no idea. I have an electric transfer pump I use to clean tankless heaters with.

The easiest thing for you to do is drain the heater, pour it in, fill the heater to mix it up. Done.

 

[Dshow]

That looks like an out drive oil pump. I would be very concerned about the pressure in the tank as well as the fittings to that pump. If it leaks... You will get a bath in very hot water... I would probably bite the bullet and shut off/remove the cold water inlet line and put it in there.

 

[HDCS18]

Turn off the cold water inlet. Disconnect it and pour fluids in through cold water inlet to heater. Then reconnect cold water line.

 

[Don_S]

Unfortunately, the inlet and outlet pipes from the heater are soldered to the copper pipes of the house plumbing, so disconnecting the cold water inlet is not an option for me.

Yesterday, I tried to flush the heater via the drain valve at the bottom, but the drain valve is completely clogged and not a drop of water came out even with the valve fully open. I suspect that there is a large build up of scale at the bottom of the heater (the heater has not been flushed in years). Not sure what to do at this point. The anode rod is probably completely shot (it also has not been checked or changed since the heater was installed in 2008). So, looks like putting in a new heater may be the best option.

 

[Dshow]

I'm just a DIYer, not a plumber, so consider that going forward...
I hate it when stuff is 'hard-wired' (or plumbed) in. I would probably make sure the water main is shut off and cut the copper pipe ~12" from the heater. Then I would get a 3/4" compression to NPT fitting and put on the copper pipe. From that fitting, I would connect a flex hose to the water heater. (I would do this on the hot and cold side). Then you would have access to the water inlet. If you have a water faucet that is anywhere lower than the heater, you could use that to drain a few gallons of water so you could add the vinegar. If this draining a few gallons still isn't feasible, these new connections could be used on the new water heater, so they're not a total waste.

Funny story - On my prior water heater, I tried to drain it and it was clogged. Not a drop would come out. "Curiosity killed the cat..." I wondered what was keeping the water from coming out... I decided to stick a long, small screwdriver in the faucet to see if I could feel it. Anyway... I broke through what was stopping it up... Water came shooting out of the valve! Good thing I was in an unfinished basement. I got it shut off, but what a mess! Lesson learned.

Update: They make a flex hose with a sharkbite connector on one end and the other end will attach to the water heater. This would eliminate the need for the compression fitting.