Advice needed- use pressure relief valve when draining heater?

[DetourDuck]

I have a three-year old, 50 gal electric water heater, with a 3/4" brass ball valve replacement for the plastic OEM drain valve.

I would like advice on how to release the vacuum in the tank when I drain it for its yearly flush. I have seen two different lines of advice online. One line of advice is to open hot water faucets, the other is to open the tank pressure relief valve. I have done it both ways, with different results.

If I open the hot faucets to both the sink and tub in the bathroom adjacent to the heater--it takes about 8 hours to drain the tank. I either have to run the drain hose out the front door--there is not enough pressure to cause the water in the hose to go over the wall of the bathtub (my nearest drain), or I have to place a bucket under the drain valve, and empty the bucket every hour or so. If I open the pressure relief valve at the top of my tank, I can drain the tank in under 30 minutes, and I can run the hose into the bathtub. Obviously, I prefer the method of opening the TPR valve.

I recently had some plumbing work done to the cold water inlet to the water heater. The plumber asked if I flushed my heater regularly, to which I replied that I did. He then cautioned that one should NEVER use the TPR valve to drain the tank. I was told that opening and closing the valve causes damage to it, or that sediment could get trapped in it, so that it would need to be replaced. I'm guessing the sediment remark does not apply to top mounted TPR valves, but does simply opening and closing the TPR valve damage it?

And if opening the TPR does damage it, is there a way to get my water heater to drain faster? Do I need to be opening all the hot water faucets, not just one or two?

Thank you so much for your help!

 

[Reach4]

He then cautioned that one should NEVER use the TPR valve to drain the tank.

To be clear, the TPR valve lever is only being used to vent the tank, and you are getting the water out of the drain valve.

I think the reason there is a test lever is to make sure it opens, and when you don't lift the lever, the valve closes. I am not a plumber, but I don't see any damage from what you do.

I am surprised that opening hot water faucets does not admit air quickly. I guess that would be the heat trap on the hot side. How about turning off the water to the house, leave supply valve to the WH open, and opening some cold faucets?

 

[Sponsor]

 

[Jadnashua]

It really depends on your plumbing layout...you'll get different results if this is a single story home versus a multi-story one, and, whether the lines ever have dips or jogs in them...a siphon isn't as fast as a flush.

You'll tend to get different end results with the life of the T&P valve depending on whether it opened itself, or you open it. It's true that the thing is not designed for regular use (like if you have a closed system without a working expansion tank, and it opens after every hot water use that causes the burner to come on), but for an annual drain, not so much. The issue is potential mineral buildup on the shaft, and because water is coming out, the potential to get crud on the sealing surfaces. That isn't as likely to happen when it's air going in, versus water coming out.

 

[Terry]

When draining/flushing a tank, I hook up the hose and open the valve to open things up. It helps blow out the sediment with the pressure on.
You can then if you want, open hot taps and then close the incoming cold to the water heater in that order. I don't like using the T&P to help drain unless I plan on replacing the water heater or the T&P at that time.

 

[DetourDuck]

Thank you for your responses!

Yes, to clarify, I am only using the T&P valve to vent the tank. I’m in a single story home, with the water heater in a hallway closet, next to my main bathroom.

My drain process: Turn off electric breaker to WH, wait a couple of hours for water to cool. Connect a hose to the drain at the bottom of the tank, turn off the cold water inlet next to the tank, open hot water faucets in the bathroom, open the tank drain, open the T&P valve. I have not had any water come out of the T&P, just a nice loud hiss as it vents.

In one of my earlier attempts to drain the tank, I did think that perhaps sediment was blocking the valve, making it slow draining, so I opened the cold water inlet to the tank and closed the hot water faucets to try to flush the sediment. That technique did give me a nice flow of water. I let the water run like this—open inlet, open drain valve—for about 5 minutes. However, after I opened the hot water faucets and turned the inlet off, the water out of the tank slowed back to a trickle. It still took hours to drain the tank.

Unfortunately, this was not enough to clear out enough sediment to stop my water heater from making popping sounds whenever it turned on. I have found that I do have to completely drain the tank and use a Shopvac (with DIY tube attachment) to suck out enough sediment to get the popping to stop.

So....the consensus seems that using the T&P to vent the WH is less than ideal.

The advice is to shut the water at the street, leave the WH inlet open and open both hot and cold water faucets to vent when I am ready to drain? Do I need to open all of my faucets? Am I understanding correctly?

Thanks again.

 

[Sylvan]

• Low-pressure steam boilers (15 psi and less) – manually check quarterly and pressure test annually
• Hot water heating boilers – manually check quarterly and pressure test annually
• Water heaters – manually check every two months and replace defective valves with a new valve if a repair or resetting is indicated

When testing the pressure relief valve, raise and lower the test lever several times.

 

[Reach4]

So....the consensus seems that using the T&P to vent the WH is less than ideal.

The advice is to shut the water at the street, leave the WH inlet open and open both hot and cold water faucets to vent when I am ready to drain? Do I need to open all of my faucets? Am I understanding correctly?

I am not sure. Others are more sure.

For opening faucets, I would think one or two bigger ones should be sufficient to admit air. The reason for the cold would be that you may have a heat trap device on your output that has some check-valve characteristics.

 

[Jadnashua]

The water comes out of the WH near the top. In a single story house, your faucets are lower. That means it is trying to siphon rather than drain which is why it is so slow. WHen you have a second story, or a basement, opening a valve above usually is more than sufficient. Yours are not 'above', which is your problem.

For a longer term solution, you could add a drain valve above the WH rather than using the T&P valve.

 

[Sylvan]

Why are so many against using the T&P for breaking a vacuum? The T&P has to be tested periodically as most codes do require and it just good plumbing practice

If the installer was decent they would install a shut off on the hot and cold and hopefully the return so the T&P just makes sense to use OR if the installer used a dialectic union instead of the dielectric nipple or even used a brass or copper union all one has to do is loosen the union above the tank and below the shut off valves and this will also allow break the vacuum

 

[DetourDuck]

The water comes out of the WH near the top. In a single story house, your faucets are lower. That means it is trying to siphon rather than drain which is why it is so slow . . .

Thank you. Your explanation was very helpful!

 

[Reach4]

Thank you. Your explanation was very helpful!

It made sense to you? It could start siphoning, but soon the water water in the pipe would be sucked out. Then air would come in. I still expect it is the heat trap slowing the air.

 

[Clog]

I've plumbed in several places to equalize pressure / admit air / prevent vacuum in the piping to HWH in order to facilitate maintenance / service.

1. Vacuum Relief Valve on inlet (automatically functions, nothing to do or turn)

2. Three way shut off valve on cold supply. (not only drains expansion tank for replacement, but can also manually admit air into storage tank)

3. Three way shut off valve at hot water piping to wall. (to drain pressure & temp gauge stack for service, and permit localized disconnection)

4. Servicing Tee at HWH outlet, with lock out ball valve above T, and threaded brass pipe blog above lock out ball valve (after following heater shut down procedures, and verifying absence of pressure with permanently plumbed gauge, the brass pipe plug can be removed, and the lock out ball valve unlocked and opened, for a straight shot into the tank to pour in Hydrogen Peroxide to mitigate sulfur smell, should it ever manifest in the future, without unscrewing the code required flexible connectors, which never seal quite right again due to the elastomeric imprint or degradation in the coupler)

5. Y screen in the gauge stack (to keep stray sediment from floating up to the gauges). There is a service port on the Y of the Y screen that can be opened where air can be admitted as well.

I'm not suggesting that you do all of these things, or any of these things in particular. I'm just sharing what I have done by way of illustration, so as to demonstrate a variety of different ways the plumbing can be set up to equalize pressure and eliminate vacuum in the water heater tank for draining purposes, without running the risk of sediment preventing the T&P valve from closing fully again.