New T&P valves on water heater leaking, pressure driven from 65 to 165psi

[Rudyard]

For my first post here - a family I know moved into a house that's three levels, garage is at ground level and has two gas water heaters, one for each flat above. Both are 48 gallons. Each has four settings: A B C and Very Hot. Both are set at A. Both tanks have brand new T&P valves.

They continue to drip. So I tested the pressure and generally get a reading of 60 to 65 psi (when a water line is open, ~40psi) I turned up tank #1 one click (B) and by the time it finished heating the pressure rose to 165, the valve started dripping at 155. I turn that tank back to A and turned tank #2 up one click. This time the pressure only went up to 161 (only!) And tank number one started dripping at 155 psi. and tank number two started dripping at 160. I didn't even want to try what would happen if I turned both heaters on at the same time.

So here are the questions:

> Is that a normal pressure range or is there a problem with the thermostats allowing too much flux in the temperature? (I didn't have anything to check the temperature so I don't know what the high/ low in a given setting is). Going from 62 to 165 seems like a lot but is this normal? (this is the big question)

> Since they have a common cold line supply, they're only about 4 or 5 feet apart is it safe to use one expansion tank- getting one that is qualified to handle 100 gallons? The tanks I've looked at seem to have a max of 150psi. Obviously that won't work.


> There are conflicting recommendations on how to position the expansion tank I would think that you would wanted pointing up so the water pushes up against the air. Maybe it doesn't matter? Does the length of the tube coming off the T going to the tank have any effect?


There is a pressure regulator at the shutoff valve. There is no expansion tank. I decreased the house pressure by about 15psi when I left.

Recap: Is this pressure range normal. New t-stats? One or two expansion tanks?

thanks

Rudy

===== A bit of history if you're bored. They had a plumber over cos there was water on the floor near the tanks. Since it was not leaking when the plumber got there he said he had no idea what it could be. Then they said the water pressure was low so he turned it up. THEN they called me, I told them it's 50% extra when I have to come in after someone else (I think this should be a standard rule). Stopped by the house, left two plastic cups with pebbles in the bottom under the discharge tubes, next morning, the floor was dry, water in cups. Changed out both TnP valves, still leaked. Tested the psi and here I am.

 

[Reach4]

They continue to drip. So I tested the pressure and generally get a reading of 60 to 65 psi (when a water line is open, ~40psi) I turned up tank #1 one click (B) and by the time it finished heating the pressure rose to 165,

Not normal! Once the pressure gets to 150, it is proper operation for the valve to release water. However it is not proper to have the pressure get that high.

There is a pressure regulator at the shutoff valve. There is no expansion tank. I decreased the house pressure by about 15psi when I left.

You need an expansion tank. Therm-X-Trol is a top brand, but will cost more. You need to get one that is big enough.

http://www.amtrol.com/support/therm_res_sizing.html is a size calculator. With 2 x 48 gallon tanks, I would put 96 into the calculator.

 

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[Jadnashua]

You likely have what is referred to as a 'closed' system. Water expands when you heat it. Pipes don't (well, not nearly as much as the water!). What you have is a very common problem that is solved by installing an expansion tank on the cold side prior to the WH(s). It must be sized properly and the precharge adjusted to your nominal pressure. Once you've done that, the leaking T&P valves should stop. Since they're new, they probably will reseal properly. If they were older, you might have to replace them again. The valve should open at 150psi or 210-degrees F, so it's obviously doing its job. Your water pressure gauge may be off slightly.

 

[Rudyard]

Thanks folks. I'll drop an expansion tank in, happy I only have to put one. Will check out the calculator tool, very cool! I'm heading over there today, I want to see what the temperature flux is, I have a feeling the one or both t-stats aren't doing their job, maybe letting the temp drop too low before they kick in, which is what's driving this degree of a pressure range.

 

[Jadnashua]

An ET is only supposed to be installed between the WH and any shutoff valves, so you might, technically, need two if the two tanks can be isolated via shutoffs. The idea is that it must be able to do its job, regardless of whether the supply is on or off. Functionally, as long as the shutoffs were open, it should work, but you'd have a code issue.

 

[Rudyard]

Thanks. I'll check the config today, I could have sworn it's a common pipe to both tanks, they sit right next to each other, but it makes sense each would have a shut off.

 

[Reach4]

Thanks. I'll check the config today, I could have sworn it's a common pipe to both tanks, they sit right next to each other, but it makes sense each would have a shut off.

I would use one tank, and don't shut the valve without turning off the heat to the WH.

 

[Reach4]

An ET is only supposed to be installed between the WH and any shutoff valves, so you might, technically, need two if the two tanks can be isolated via shutoffs. The idea is that it must be able to do its job, regardless of whether the supply is on or off. Functionally, as long as the shutoffs were open, it should work, but you'd have a code issue.

Do you have a code citation for that?

The reason I ask is that I am skeptical. If what you say were true, it should follow that everybody would need a thermal expansion tank -- even those on not-closed systems or those with wells that have really big pressure tanks.

 

[Jadnashua]

Code requires you to install devices per the manufacturer's instructions...read any ET installation instructions.

 

[Reach4]

Code requires you to install devices per the manufacturer's instructions...read any ET installation instructions.

OK. Try this one: http://media.wattswater.com/1915323.pdf

 

[Jadnashua]

OK. Try this one: http://media.wattswater.com/1915323.pdf

Do you seen any valve between the tank and the WH? If it was allowed, it would show up as either required or optional.

 

[Reach4]

You are still making stuff up, and presenting it as fact/law.

 

[Jadnashua]

I used to advocate a valve to make it easier to remove and replace the tank when time came to service it when, I'm pretty sure it was HJ, chimed in, saying that was not allowed. That, along with the diagrams on their installation instructions which do not show one, back up my claims. I think if you do a search, you'll find others in the trade also backing that premise up.

The AO Smith instructions are a bit more explicit http://www.hotwater.com/resources/l...max®-expansion-tanks-pmc-manual-(0002911480)/

The Amtrol shows a similar installation diagram

http://www.amtrol.com/media/documents/thermxtrol/9015087_06_16_Thermal_Expansion_Tank_IO_.pdf

where there is no shutoff between the tank and the ET. Both of those also specifically say it must be between the WH and any check valve. You could consider an on/off valve an absolute check valve.

 

[Reach4]

A valve on the incoming water to a WH is really handy when flushing the WH. Heat off of course. HJ said stop valves on the WH incoming water supply are not permitted? I would find that surprising, but I have been surprised before.

The AO Smith instructions are a bit more explicit http://www.hotwater.com/resources/l...max®-expansion-tanks-pmc-manual-(0002911480)/

Says check valve or backflow prevention device.

Both of those also specifically say it must be between the WH and any check valve. You could consider an on/off valve an absolute check valve.

Those are pretty smart people. If they say check valve, I think they mean check valve. I won't consider an on/off valve to be a check valve. I think a check valve is a one-way valve. I have a WH incoming shut off valve. If I were putting in a new WH, I would still have a shut off valve. I don't have a thermal expansion tank, although I have a 44 gallon pressure tank on my incoming water.

 

[Jadnashua]

Nothing says you can't have a shutoff valve (at least most places) on the inlet to the WH (and neither did I)...it's just that none of the ET manufacturers show one between the WH and the ET, and that's for a reason. HJ's comment, if I remember it correctly, was quite awhile ago where he said you should not have any valve of any type between the ET and the WH.

 

[Rudyard]

Thanks for all your help folks. I was only able to stop by the house for a few minutes for a different matter. On the older, crankier heater I tested the water by filling a slightly pre-warmed coffee mug from the drain valve, note- I don't think it had fully cooled down. It was at 99.1 degrees, I tripped it to come on and it turned off at 127. Yeah, basically a 28 degree jump. I have searched everywhere to see what temp range a heater allows for any given setting. No info. I'm testing my own heater today. -Rudy

 

[Jadnashua]

What the calculator is asking for is the difference between your incoming, cold water supply, and the temperature you set the WH to. Depending on where in CA you are, the seasonal changes in the incoming water may not have large swings, but where I live, I've actually measured incoming water at 33-degrees after a long cold spell, but in the summer during a heat wave, it can be in the mid-70's. Say you set the WH to 130, that could be nearly a hundred degree swing, or about half of that. The ET needs to be sized for the worst case. IN reality, bigger doesn't hurt, too small does. They do get more expensive as they get larger, but for what a typical home would need, it's not much.

 

[Rudyard]

Good info. I live in SF. Some years we have a warm week or two in February, and then the second part of our summer is usually in September, where it's usually warm for about 3 to 5 days and then foggy for one or two, and so on. Seasons do occur once you get about 40 minutes out of the city. I doubt the ground temperature changes by more than a degree or three in a given year. So that's great -I'll test the temperatures today.

 

[Rudyard]

Good info. I live in SF. Some years we have a warm week or two in February, and then the second part of our summer is usually in September, where it's usually warm for about 3 to 5 days and then foggy for one or two, and so on. Seasons do occur once you get about 40 minutes out of the city. I doubt the ground temperature changes by more than a degree or three in a given year. So that's great -I'll test the temperatures today.

I am still wondering if that temperature difference is normal, seeing as it's creating that wild pressure swing

 

[Jadnashua]

The pipes expand MUCH less than the water...any expansion translates to pressure increases.