hot water tank..new vs old

For the past 40 years I have installed 4- 40 gallon hot water tanks (natural gas) in my home. Today I picked up a new 30 gallon tank, installed it, fired up and could not believe the pressure rise as temp increased, went to 140# and still going at

120 deg temp My incoming pressure is usually 90psi, give or take 10 # I know I am going to need a press reducing valve, either for the entire system, or the hot water tank itself, or an expansion tank for the hot water tank. Question is why in the world am I having pressure rises like this on the new tank, and never had this problem before ? thanks
Reply to
jimmy
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Your water heater cannot create a system pressure rise unless your water system is a "closed" system.

Do you have a check valve or back-flow preventer somewhere in the system? If so you need a system pressure relief valve or an expansion tank.

Run some water out of a hot water valve in the bathroom or kitchen (about gallon or so) and see if the pressure drops.

My best guess is that the expansion of the water in the water heater from cold to hot is pressurizing a closed system.

cheers Bob

Reply to
DD_BobK

Sounds like you have a check valve in the supply line to your hw heater. You should install an expansion tank on the line at your hw heater. They make small ones that can be supported by copper pipe without additional bracing. If you have some other piping you may need to support it. Lowes and home Depot both usually carry them. Typically around a $100. If you are on a well then your normal storage tank should handle the expansion. Look for a chack valve somewhere between the hw heater and the well tank.

Reply to
jamesgangnc

jimmy wrote: ...

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I'd venture the existing PRV has failed and you weren't aware of it before...

90psi is about double what normal residential water pressure is. Amazing haven't blown toilet valves, icemaker, washing machine control valve, etc., etc., etc., ...

Any water system is a "closed system" when not running; otherwise there's no holding it in.

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Reply to
dpb

Some water heaters come with a connector nipple on the cold side (inlet) that have a plastic ball in them that acts as a check valve.

Reply to
Molly Brown

No, few suburban household water systems are "closed". The service entrance means it's not closed. For many years hw expansion pressure was absorbed by the service line coming in. Rural might satisfy the definition of closed but well systems almost always have storage tank that doubles as an expansion tank.

Reply to
jamesgangnc

Back flow preventers have been in the code for years. Most services are not "open" if you live in a fairly new neighborhood. The pressure rise should go away immediately as soon as he opens a hot water valve.

Reply to
gfretwell

jamesgang has the correct answer. your new heater has a check in the inlet. Take it back apart and throw the somebeach in the round file. THEN put an expansion tank on, (anywhere in the entire system is fine, they don't have to be right next to the heater).

Reply to
Steve Barker

Reply to
jimmy

there's no holding it in.

Reply to
DD_BobK

message

Water hammer minimization suggests limiting supply pressure to 65 psi max.

cheers Bob

Reply to
DD_BobK

I think it's safe to say that well in excess of 90% of suburban homes still have nothng between them and the city water supply. The op found out he does have one. But I can tell you my neighborhood of

1,200 homes was built within the last 20 years and none of them have a check valve, regulator, or backflow preventer between the city supply and their water system. Except for irrigation.
Reply to
jamesgangnc

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