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Old 04-12-2012, 06:50 PM   #1
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How to best purge a hot water tank


Day 6 of owning our first house (1920-1930's Colonial) and we finally have hot water after replacing the transformer. But now we have an issue there is a ton of sediment and rust in the system.

Not sure how long the system sat dormant, at least 6 months, could be a year or more. There is a relief system on the tank, but it still does not cover the bottom 1/4 of the tank, and it's awfully close to the oil pump and transformer so I don't want to go that route unless there is no other option.

Is my only option just just constantly run the hot water till the system is purged?

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Old 04-12-2012, 06:55 PM   #2
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How to best purge a hot water tank


At the bottom of the tank you'll find a valve with a hose thread end.
Put a hose on it and point the other end somewhere it's OK to get flushed with water and crap.
Flush the water and crap out of the WH.

That's about it.

(Ideally, the valve is a good brass boiler type that the previous owner
had the foresight to install when the WH was brand new.)

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Old 04-12-2012, 07:14 PM   #3
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How to best purge a hot water tank


One way to clean up the bottom portion of the tank (where the sediment accumulates) would be to drain all of the water out of the water heater, flush the bottom portion, and then fill it back up again.

Maybe try this:
1. Turn off the water heater so the elements won't burn out.
2. Turn the valve that feeds cold water into the heater off.
3. Connect a hose to the drain valve on the side of the tank close to the bottom to allow drainage to an acceptable place. The hose should all be lower than the drain valve.
4. Open the heater's drain valve to release any built up pressure in the system. You might need a screwdriver to open the valve, depending on the type of valve.
5. Open the the pressure relief valve (T&P valve) on the heater.
6. Drain all of the water out of the heater.
7. With the heater's drain still open, fully open the input water valve for a short time and then turn it off and let the water drain out. This will allow the incoming water pressure to flush out the bottom portion of the tank.
8. Repeat step-5, varying the time of water input as you feel appropriate, until the water runs clear.
9. Close the drain valve.
10. Close the pressure relief valve on the heater.
11. Open the hot water faucet in your laundry room (which should have 2 handles (hot and cold) and not be a single handle faucet).
12. Fill the heater until the water out of the faucet runs solid and clear with no air bursts.
13. Remove the aerators on every hot water faucet and run them to clear any air pockets and discolored water remaining in the pipes.
14. Turn the water heater back on.

HRG

Last edited by Homerepairguy; 04-13-2012 at 09:08 PM. Reason: Added steps 3 and 4. Also added aerators to step-13.
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Old 04-12-2012, 07:20 PM   #4
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How to best purge a hot water tank


Just curious, would it be worth injecting somehow a cleaner like CLR or something into the tank to break up the calcium deposits? Just curious.
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Old 04-13-2012, 06:18 AM   #5
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How to best purge a hot water tank


I would not put any "chemicals" into the hot water tank. It would take a few tankfuls of water emptied in turn completely via the tank drain valve to "rinse" out any remaining chenicals when you are done.

I would not open the pressure/relief valve (step 3 above) that soon; water could get all over the floor Opening up faucets should be enough to admit air to allow the tank to drain.
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Old 04-13-2012, 05:03 PM   #6
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How to best purge a hot water tank


Quote:
Originally Posted by AllanJ View Post
I would not put any "chemicals" into the hot water tank. It would take a few tankfuls of water emptied in turn completely via the tank drain valve to "rinse" out any remaining chenicals when you are done.

I would not open the pressure/relief valve (step 3 above) that soon; water could get all over the floor Opening up faucets should be enough to admit air to allow the tank to drain.
I agree about not putting any chemicals into the tank.

Regarding step-3 (now step-5), you have a point. I will add a step to open the heater's drain valve first to release any built up pressure.

Regarding opening faucets to drain the heater. I've found when I've drained our water heater that there's a huge difference between using the pressure relief valve to let air into the tank verses using hot water faucets. Water drains out of the tank "really, really" slowly when just opening hot water faucets.

Our single story home is on a concrete slab and the top of the water heater is the highest point in the plumbing. Water has to be sucked up from under the slab to above the water heater. It is excruciatingly slow using open hot water faucets. Of course cold water faucets can't be used since the cold water input valve to the water heater is turned off.

Also, if the water heater has a heat trap "valve" above it in the hot water line, water will not be allowed back into the water heater from the hot water line. No drainage of the tank will occur. We don't have heat trap "valves" in our lines so that's not why our heater drains so slowly using open hot water faucets.

Opening the pressure relief (T&P) valve on the heater is the sure way to allow air into the heater for drainage. If the heater is in the basement and there's no heat trap in the line, then opening hot water faucets on upper floors would probably work fine. But all of the above (including single story homes on concrete slabs) requires additional explanation for draining the tank. Some folks won't even know if they have a heat trap valve in their hot water line.

Best regards,
HRG

Last edited by Homerepairguy; 04-13-2012 at 08:56 PM.
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Old 04-13-2012, 05:45 PM   #7
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How to best purge a hot water tank


So I have done the steps recommended, minus releasing the pressure valve because that is literally right next to my transformer and oil pump. The tank drained slowly, but I let it run through 5 flushings. Ran the water till it ran clear, let it go another 10 minutes, and then kicked the hot water back on. All was well, so I started another project.

The process took about 3.5 hours in total.

Came back 2 hours later, and the water is running dirty again, almost as dirty as before.

Thoughts?
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Old 04-13-2012, 07:40 PM   #8
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How to best purge a hot water tank


Do you have steel pipes? If so until there replaced it's going to happen.
Also you should have removed all the airiators on the faucets or there going to plug up while the waters being flushed out.
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Old 04-13-2012, 08:55 PM   #9
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How to best purge a hot water tank


Quote:
Originally Posted by LTParis View Post
Came back 2 hours later, and the water is running dirty again, almost as dirty as before.
Thoughts?
Only hot water or both hot and cold water?

Joe,
Good point about removing the faucet aerators. I'm going to add that to the directions I posted.

Thanks
HRG

Last edited by Homerepairguy; 04-13-2012 at 09:06 PM. Reason: added point about faucet aerators.
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Old 04-14-2012, 07:49 PM   #10
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How to best purge a hot water tank


Only hot. I thought for a second that I might be just getting kickback from the drain, but I stopped it and no luck.

The amount of sediment changes almost every time. One second it's just a little to significant discoloration. Since one of my bathroom tubs has signifigant pressure, and also has an individual hot line to the tub, it's the one I have been using to try to purge out.

Could I put a hose to the tank again, drain it, but then let the cold line back open for a good while to flush it more? I am concerned that the drain is really not low enough to really allow for the sediment to fully get out. I had thought I had the system flushed before but no luck.

Another wrench into this is the system is a oil tank, not gas or electric, and I just got a new transformer for it on Thursday. I really would like to switch to gas ASAP, and there is a gas line coming to the house but it's not utilized, so I am not sure how long it would take to get gas turned up.

If I have to switch to a new tank, I am also left with the question, tankless? Tank? Hybrid?
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Old 04-14-2012, 10:36 PM   #11
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Quote:
Originally Posted by LTParis View Post
Only hot. I thought for a second that I might be just getting kickback from the drain, but I stopped it and no luck.

The amount of sediment changes almost every time. One second it's just a little to significant discoloration. Since one of my bathroom tubs has signifigant pressure, and also has an individual hot line to the tub, it's the one I have been using to try to purge out.

Could I put a hose to the tank again, drain it, but then let the cold line back open for a good while to flush it more? I am concerned that the drain is really not low enough to really allow for the sediment to fully get out. I had thought I had the system flushed before but no luck.

Another wrench into this is the system is a oil tank, not gas or electric, and I just got a new transformer for it on Thursday. I really would like to switch to gas ASAP, and there is a gas line coming to the house but it's not utilized, so I am not sure how long it would take to get gas turned up.

If I have to switch to a new tank, I am also left with the question, tankless? Tank? Hybrid?
Dirty water out of the hot water line only sure sounds like a dirty water heater tank problem. I'm not familiar with an oil tank heater so I'll bow out at this point. Hopefully someone that is familiar can help you out.

Regarding switching to a tankless water heater. First decide whether it will be gas or electric. If gas, find out how what size the gas line has to be for a gas tankless heater. If electric, find out what the input amperage is required for that.

When I researched an electric tankless water heater for our 40 year old home, I discovered that I would have to upgrade the capacity of the power line (from the utility power line to our home's switch box and from the switch box to the circuit breaker panel) to handle the high demand. The cost of doing that was too prohibitive so I went with a solar water heater with normal electric heating backup.

Best of luck,
HRG
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Old 04-15-2012, 06:18 AM   #12
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How to best purge a hot water tank


Quote:
Originally Posted by LTParis View Post
There is a relief system on the tank, but it still does not cover the bottom 1/4 of the tank, and it's awfully close to the oil pump and transformer so I don't want to go that route unless there is no other option. ?
By the way, a pressure relief valve can be anywhere in the plumbing system and will protect the entire water heater tank so long as there is no closed valve or check valve between it and the water heater. With all faucets turned off the pressure is the same everywhere in the system

The relief valve is in the water tank near the top to provide overtemperature protection as well. Hotter water tends to rise in the tank. The kind of relief valve used has a probe with expanding liquid inside similar to a thermometer and that pushes the valve itself open when the temperature gets to a certain level.

You can drain the tank down to 1/3 to 1/4 remaining and then alternately pump water into the water heater drain valve to churn up the sediment and then drain some back out. The water heater heat must be off during this operation and not turned on until the tank is full and water is running from a hot faucet upstairs. You will need a garden hose section with two female ends to connect the hose end coming from a garden hose bibb to the hose end coming from the water heater drain during the pump in sessions.
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Last edited by AllanJ; 04-15-2012 at 06:23 AM.
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Old 04-16-2012, 02:20 PM   #13
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Well it seems I have tried everything, and no luck. The tank is too old to really put additional effort into it. I can only imagine how much my water bill will be just for this. <smh>

Seems oil fired water heaters are quite expensive, so I (with the plumbers as my proxy) are exploring gas options. There was a gas line that ran to the house, but no one is sure of the condition. Might be a couple weeks to get this resolved but I'll have a more sound mind in the end.
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Old 04-17-2012, 12:57 PM   #14
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So I am really stuck now. Talked to my plumber who is trying to help me out to get some resolution.

1. Gas. Really want to go gas route, but our provide Central Hudson could take 6+ plus just to get to our site. That means 6-8 weeks or more not being able to live in our house. And there is the cost of new piping from the feed to the hot water heater and future-proofing the system to accept new feeds for our stove, heater, and drier.

2. Electric. Current panel is only 100A and last I checked I don't think I have two slots for a 30A breaker (let alone the current for it). We had plans to rewire the house and jump to 150A or 200A service, but that is June/July timeframe. Plus I am sure there would be a signifigant cost to electrive v. gas for the hot water tank.

3. Oil. Unit is very expensive, and oil is very expensive. I can get it done now but my plumber and a couple others are telling me to not go this route.

3 crappy choices. Opinions?

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