RV water heater check valve install

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Pinecone

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I am replacing a plastic check valve on the output of a Dometic RV water heater. The new check valve is brass which presents a problem of dissimilar metals and galvanic corrosion. I thought a CPVC nipple between the tank and the check valve would work to insulate the two materials, however I can't find a CPVC 1/2" nipple rated for hot water. The companies that manufacture them state that because the fitting is threaded, they are only rated for cold water use.

I'm wondering if there are nylon or PVC fittings rated for hot water. If not any suggestions would be appreciated. The water heater is set at 140 degrees F.
 

Jeff H Young

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Use a brass nipple and with brass check valve you dont want plastic at the tank
 

John Gayewski

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Stainless steel nipples also works well. Or a dielectric union threaded on one end.
 

Pinecone

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Is there a dielectric union with galvanized threads? I cannot use any other material or corrosion will be an issue.

A brass nipple is suggested, but will not solve my problem
 

Jeff H Young

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Whats the problem that 1/2 " cpvc nipple would fix that a brass nipple wont fix ? something very unusual about this steup
 

John Gayewski

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Is there a dielectric union with galvanized threads? I cannot use any other material or corrosion will be an issue.

A brass nipple is suggested, but will not solve my problem
Yes there are threaded dielectric unions
 

Pinecone

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Jeff H......the problem is galvanic corrosion, i.e dissimilar metals. Plastic is non-conductive. Brass is conductive, hence corrosion. Now, apparently there are no PVC or CPVC threaded fittings that are recommended to be directly fitted to water heater output, because of expansion/contraction leading to deterioration of the adapter.
 

Pinecone

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I may have found a solution. PEX male adapters and a short re-plumbling job with PEX tubing. The male 1/2" adapter is rated to 200F.

I read where you are not supposed to use PEX fittings right at the water heater output, but this seems to be because of the exhaust flue. In my case the WH output is on the back and the exhaust is on the front (venting outside the RV). So I see no reason to have to extend a pipe out from the heater before converting to PEX. Am I correct?
 

Jeff H Young

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Id use the brass shouldnt be a problem. run it all the time to reduce corrosion
 

John Gayewski

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I may have found a solution. PEX male adapters and a short re-plumbling job with PEX tubing. The male 1/2" adapter is rated to 200F.

I read where you are not supposed to use PEX fittings right at the water heater output, but this seems to be because of the exhaust flue. In my case the WH output is on the back and the exhaust is on the front (venting outside the RV). So I see no reason to have to extend a pipe out from the heater before converting to PEX. Am I correct?
Code doesn't allow pex on a water heater. Not only because of the flue. Pex isn't strong enough in a malfunctioning water heater.
 

Jeff H Young

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ne3ver seen a waterheater that a brass nipple would be improper to use brass to copper brass to galvie its all good
 

Pinecone

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Code doesn't allow pex on a water heater. Not only because of the flue. Pex isn't strong enough in a malfunctioning water heater.
What is a "malfuntioning" water heater. I can see strength needed in a residential water heater in case there was movement. The RV water heater is different in so far as there can is no physical movement. It's a square box mounted solid. Maybe a little bit of movement in the line as you go down the road but minimal, and certainly exerting no force on the fitting.

Virtually all RV's are now plumbed using PEX, but I'm obviously new to working with it. I want to make sure I do this right.
 

John Gayewski

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What is a "malfuntioning" water heater. I can see strength needed in a residential water heater in case there was movement. The RV water heater is different in so far as there can is no physical movement. It's a square box mounted solid. Maybe a little bit of movement in the line as you go down the road but minimal, and certainly exerting no force on the fitting.

Virtually all RV's are now plumbed using PEX, but I'm obviously new to working with it. I want to make sure I do this right.
Use metal flex lines then pex. That would be right. Pex on a water heater isn't right. I don't have time to argue and explain about t&p valves and runaway water heaters.
 

Reach4

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If this is a propane WH, you certainly want to keep pex away from the flue.
 

JerryR

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This is an RV water heater. It has an aluminum tank without an anode rod. That is why they use a plastic check valve to prevent dissimilar metal corrosion.
 
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