Gravity recirc stopped working

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Jon229

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I've been using a gravity recirc loop (60 ft from tank to last fixture) on my water heater for several years. It worked very well. Bottom of the tank is about 8 ft below the supply & return lines.

I had my 18 yr old gas Rudd tank replaced with a new Bradford White M2XR504 and now my recirc loop no longer works. The Plumber made sure there is no air in the return line. The return line gets hot when the water is used so there doesn't seem to be a blockage anywhere.

There is a swing check valve near the tank drain connection. I confirmed the arrow is pointing towards the tank. A week after tank installation, I removed & drilled a 1/8" hole in the swing plate of the check valve to facilitate flow which is a recommendation I read. That didn't help.

Is there something in the manuf of new tanks (or the tank I have) that might prevent it from working with a gravity loop? I can't figure why else a system that worked well suddenly does not work merely by replacing the tank.

Jon
 

JohnjH2o1

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There is air in the line. The sure way to remove it is to have a drain valve on the return line, on the house side of the check valve. Connect a hose to the valve to purge the air out of the line.
 

Jon229

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There is air in the line. The sure way to remove it is to have a drain valve on the return line, on the house side of the check valve. Connect a hose to the valve to purge the air out of the line.
Thank you. I will try purging again. I have a drain valve installed between the check valve & a stop valve located on the heater side. Is there a reason this would not work as well as a drain on the house side of the check valve?
 

JohnjH2o1

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With the drain on the heater side your not purging the recirculation line, your pulling the water out of the heater, not through the recirculating line.
 

Jon229

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With the drain on the heater side your not purging the recirculation line, your pulling the water out of the heater, not through the recirculating line.

Sorry I didn't explain myself well enough. The return line from furthest fixture-> ball valve->swing check->drain->stop valve->T into heater & bottom drain. I will purge it again, but it's been done several times without solving my problem.

I should say that the above mentioned drain & stop valve after the check valve is actually a stop waste valve with the valve drain port on the return line side of the valve. I close the valve to shut off the flow from the heater and I use the waste port to purge. Last time I did this I ran about 4 gallons which should be sufficient for the 60 ft of 1/2" copper from the furthest fixture.

jon
 

JohnjH2o1

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If your trying to purge it with the just the small cap on a stop & waste valve your not getting enough volume to purge the line.
 

Jadnashua

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The new WH may have a different style heat traps on the in/out fittings that may be enough restriction to let your gravity system work.
 

Jon229

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The new WH may have a different style heat traps on the in/out fittings that may be enough restriction to let your gravity system work.

Interesting idea. Do you know of a way I can verify that? I'll feel the outlet pipe in the morning before everyone starts using the fixtures.

Jon
 

JohnjH2o1

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In order to purge the line you need the volume of the full pipe. The hole behind the cap is 1/8" at the most.
 

Jadnashua

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Interesting idea. Do you know of a way I can verify that? I'll feel the outlet pipe in the morning before everyone starts using the fixtures.

Jon
Many WH come with heat traps. If yours did, and they were installed, that could stop the gravity circulation (that's what they are designed to do!). If they are there, you may have to remove them to make it work. The manual should indicate whether they are there, and a picture may confirm that information. Normally, they do help to save some energy, as constantly circulating the water means you have fairly long radiators.
 
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