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Expansion tank causes meter to turn?


Lasswell
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Can someone 'splain to me why there is an expansion tank and a mixing valve on a DWH? Is this a Left Coast thing? Even in a really tiny house there is generally enough pipe length in the distribution lines to accomodate the expansion, and there's no need to temper the water unless the temps are cranked up for hydronic heating. Around here this set up would be used to manage the constantly varying high limit of a solar thermal DHW system, but only if the tank was used for both domestic (the tempering valve) and solar storage (the expansion tank).

In response to the OP, what is the air pressure in the expansion tank? Increasing the the air pressure should solve your problem, that is after all what you are doing by capping it. When did you measure the water pressure? If you measured it at a period of even moderate demand, it likely goes much higher than 83 pounds at periods of no demand. If it were mine, I'd leave it capped or max the air pressure until I could get a PRV installed, and request a new water meter while I was at it, just to be sure.

Tom

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I have an answer, not sure if it is accurate but it is entertaining. After making a half dozen phone calls to different people at Seattle Public Utilities it spoke with one of their plumbing inspectors. I am not sure what they inspect because they are not code inspectors. She informed me that it was in fact the expansion tank pushing water back and forth through the meter as the line pressure fluctuates. They are aware of the problem and told me to remove the expansion tank. She said "I don't understand why everyone installs these on their hot water systems because they are not needed" I felt like saying (I was frustrated by this point) HEY LADY, "PEOPLE INSTALL THESE BECAUSE THEY ARE REQUIRED BY CODE" but I didn't. Just to be sure I called the plumber who did the installation and he confirmed for me that they are required by code.

So now I have the Seattle DPD (building department) telling me I have to have and expansion tank and Seattle Public Utilities telling me to remove it. I asked her to send me something in writing on this and she is mailing a letter informing me to remove the pressure tank.

I will be installing a pressure regulator this week which should take care of the problem now I just have to try to get back 6 months worth of overcharges from Seattle Public Utilities.

Thanks for your input and pontification on this matter.

John

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Well, that's certainly a new one on me. It's more than just a "code" - please inform this young lady that the mere fact of heating water causes expansion - a pound is a pound the world around.

I was going to write a lengthy dissertation about expansion tanks however I'm in the middle of a bad case of writers block.

I wonder what's for dinner?

I'll advise my customers to remove their expansion tanks immediately if not sooner.

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. . . I will be installing a pressure regulator this week which should take care of the problem now I just have to try to get back 6 months worth of overcharges from Seattle Public Utilities. . .

I suggest that you install a pressure regulator that includes a bypass that will bleed water back to the street side if the pressure on the house side every exceeds the pressure on the street side. (Did I write that right? Make sense?)

Some PRVs include bleeders and some don't. You have to look at the catalogue to know for sure.

- Jim Katen, Oregon

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Speaking from common sense.....If an effective check valve is installed on a fresh water supply system that could potentially become a totally closed system, such as when no valve outlets are open, then it would make sense to install a device that would prevent over pressurization of the system that might result from elevating temperatures. These elevating temperatures could result from the water heater, a change in seasons or other reasons.

To me, codes should bend to common sense instead of vice versa, or is this just another case of a sarchasm?

Marc

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. . . I will be installing a pressure regulator this week which should take care of the problem now I just have to try to get back 6 months worth of overcharges from Seattle Public Utilities. . .

I suggest that you install a pressure regulator that includes a bypass that will bleed water back to the street side if the pressure on the house side every exceeds the pressure on the street side. (Did I write that right? Make sense?)

Some PRVs include bleeders and some don't. You have to look at the catalogue to know for sure.

- Jim Katen, Oregon

Jim, (not trying to be argumentative) the purpose of the expansion tank is to allow for expansion. What about backflow preventer's?

There are billions of structures with hot water tanks and hydronic heating systems. We don't want boiler water backing up into our potable water system with all the nasty water treatment chemicals. Enter the expansion tank (besides their primary function of allowing for expansion).

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Speaking from common sense.....If an effective check valve is installed on a fresh water supply system that could potentially become a totally closed system, such as when no valve outlets are open, then it would make sense to install a device that would prevent over pressurization of the system that might result from elevating temperatures. These elevating temperatures could result from the water heater, a change in seasons or other reasons.

To me, codes should bend to common sense instead of vice versa, or is this just another case of a sarchasm?

Marc

Don't the codes already require exactly what you described?

- Jim Katen, Oregon

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. . . I will be installing a pressure regulator this week which should take care of the problem now I just have to try to get back 6 months worth of overcharges from Seattle Public Utilities. . .

I suggest that you install a pressure regulator that includes a bypass that will bleed water back to the street side if the pressure on the house side every exceeds the pressure on the street side. (Did I write that right? Make sense?)

Some PRVs include bleeders and some don't. You have to look at the catalogue to know for sure.

- Jim Katen, Oregon

Jim, (not trying to be argumentative) the purpose of the expansion tank is to allow for expansion. What about backflow preventer's?

There are billions of structures with hot water tanks and hydronic heating systems. We don't want boiler water backing up into our potable water system with all the nasty water treatment chemicals. Enter the expansion tank.

You put the backflow protection near the device that requires it. No need to put it at the meter.

- Jim Katen, Oregon

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. . . I will be installing a pressure regulator this week which should take care of the problem now I just have to try to get back 6 months worth of overcharges from Seattle Public Utilities. . .

I suggest that you install a pressure regulator that includes a bypass that will bleed water back to the street side if the pressure on the house side every exceeds the pressure on the street side. (Did I write that right? Make sense?)

Some PRVs include bleeders and some don't. You have to look at the catalogue to know for sure.

- Jim Katen, Oregon

Jim, (not trying to be argumentative) the purpose of the expansion tank is to allow for expansion. What about backflow preventer's?

There are billions of structures with hot water tanks and hydronic heating systems. We don't want boiler water backing up into our potable water system with all the nasty water treatment chemicals. Enter the expansion tank.

You put the backflow protection near the device that requires it. No need to put it at the meter.

- Jim Katen, Oregon

I've always seen backflow preventer's at the main in commercial/industrial applications. Fact is you don't want anything backing up into the main.

But you are correct - you can put a backflow device on the water feed for a boiler and it will suffice.

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  • 5 weeks later...
  • 6 months later...

I am currently seeing exactly the same problem on my house in Florida.

Code requires a new water heater to be installed with an expansion tank. My house was built in 1961, before code required back-flow preventers. I installed a new water heater not too long ago and because I'm a good guy, I did it per code. I even adjusted the air pressure in the expansion tank to match the water pressure per the instructions included with the expansion tank.

My water meter has a small wheel with a red triangle on it. With everything turned off in the house (including the valve to the RO system), I can see the red triangle turn forward a little bit, and then backward a little bit. However, it doesn't turn as far backward as it does forward. My meter slowly moves forward.

I've read that some meters will read reverse flow while others will now. However, NONE of them will ACCURATELY measure reverse flow. So what is happening is that the water main pressure is fluctuating causing the expansion tank to expand and contract. The water flows in and gets measured correctly by the water meter. Then, it flows back out and gets incorrectly measured. The net result is that I am paying for water that I am not actually using. I have verified this using the same method that the original poster did... remove the expansion tank.

So... this weekend I will be installing a dual check valve at the meter... which I purchased for a whopping $22.00 at Home Depot. It should pay for itself in just a few months.

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  • 10 months later...

Hi,

I believe I'm seeing exactly the same problem as Lasswell and Barnabas1969.

Background - we recently moved to a new house, and soon realised that our water bills were astronomical. We assumed a leak but have not been able to find anything. We switched off taps to all toilets and fittings that we could, but could not identify the problem, and no sign of leaks anywhere. However according to the meter, we were using about 6 Litres of water an hour even though nothing was on.

I noticed while watching the water meter that when there was nothing running the it would slowly drift backwards and forwards.

My theory was that perhaps the mains pressure is fluctuating slightly, and the expansion tank is pushing water back through the meter during the pressure drops. That combined with the possibility the meter does not measure backwards accurately. Reading this post has made me think this is the most likely explanation. However, there is a check valve and PRV in line before the water heating system with the expansion tank - so this has me stumped.

@Barnabas1969 - did the installation of the double-check valve at the meter solve your problem?

Thanks,

S

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  • 8 years later...
  • 1 year later...

My neighbor and I have both experienced this expansion tank phenomenon after getting new water heaters with expansion tanks, when previously we didn't have them. Apparently(?) they are not needed in an open system the lets the hot water expansion push back out to the street. When an expansion tank is on such a system, and if it is pressurized nearly equal to the incoming pressure, fluctuations in incoming street pressure can fill and empty the tank continuously. Since the meters in our case won't reverse, our water bill included the frequent fills. To solve this, my neighbor installed a check valve. I simply added extra air pressure to the tank (50psi vs the 42psi incoming).  In both cases, the leak detector meter stopped spinning. But what I don't understand,  is wouldn't the same thing happen without an expansion tank in an open system? Wouldn't the fluctuations in the mainline pressure cause water to flow from the hot water tank back to the street when pressure drops and then back into the hot water tank when pressure increases again? 

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