Water heater pressure relief leaks ONLY when bathtub in use

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Eliteconcept

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Hi all
Just bought our house in June. Since then I've found the natural gas state water heater ( 3 years old) leaks out of the pressure relief valve ONLY when one of the bath tubs is used. It does not leak any other time but when we give our daughter a bath.

There is an expansion tank installed on the water heater.

There is a hot water circulator installed near the water heater that serves the shower (separate from the tub) and sinks in that bath room. However due the pump being identified as causing excessive gas usage (nearly double normal usage) I have turned that circulator pump off and bypassed it.

I have drained and flushed the water heater.

The valve does not appear to leak when other sources of hot water (shower) are used.

What's going on here?
 

Reach4

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Common. Thermal expansion. You need a sufficiently sized thermal expansion tank. If you have such a tank, it has failed.
 

Reach4

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The expansion tank should be empty of water most of the time. Knock on the tank, and it should sound empty. If the valve is on top, you should still be able to tap the tank to get the empty sound. If you dribble water from a faucet, you will not have thermal expansion raising the pressure from what the city provides. It is when you stop using water, and the hot water that you put into the tub that was replaced with cold water, the replacement water expands.

Air precharge is normally checked and set while the water pressure is zero. The precharge should be at the pressure that the incoming water maxes out at.

Jeff points out that the T&P valve could be releasing water too much below the nominal 150 psi. If you get a garden hose thread pressure gauge, you can put that onto the WH drain valve. If you check that valve while the water is actively dribbling out, you can see what pressure the T&P releases at. Those gauges are under $20 and pretty widely available at a hardware store, home center, garden shop.

Does your Schrader valve hang down? If so, and if water comes out, tank is bad.
 

Eliteconcept

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No the expansion tank valve is pointing up. I am on well water not city if that matters.
When the water heater was running just now and I tapped the expansion tank it did not sound empty or hollow in any way. It made a very solid full noise


Should the expansion tank pressure be checked with a faucet in the house on?
 

Reach4

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No the expansion tank valve is pointing up. I am on well water not city if that matters.
When the water heater was running just now and i tapped the expansion tank it did not sound empty orvhollow in any way. It made a very solid full noise


Should the expansion tank pressure be checked with a faucet in the house on?
The fact that you are on well water is very significant.

Usually with well water you don't need a separate thermal expansion tank. But you have one, and it appears have failed. A thermal expansion tank is needed if there is a check valve between the well pressure tank and the WH. A check valve could be there for a few reasons. Some iron filters have those. Also, sometimes a check valve is added to prevent phantom water use detected by the softener, due to expanding water flowing thru the turbine and being interpreted as water used. Softener turbines don't distinguish direction of flow. That causes the softener to regen earlier than needed. Most of us with softeners with wells figure that is a small factor, and don't have the check valve.

For whatever reason, I think you have a check valve. A thermal expansion tank on such a system should have air precharge set to the highest pressure that the well pump system makes. If you have a 40/60 psi pressure switch, set the air precharge on the thermal expansion tank to 60 or 61. Air precharge on a thermal expansion tank, or for the well system pressure tank, is measured and set while the water pressure is zero.
 

Eliteconcept

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The fact that you are on well water is very significant.

Usually with well water you don't need a separate thermal expansion tank. But you have one, and it appears have failed. A thermal expansion tank is needed if there is a check valve between the well pressure tank and the WH. A check valve could be there for a few reasons. Some iron filters have those. Also, sometimes a check valve is added to prevent phantom water use detected by the softener, due to expanding water flowing thru the turbine and being interpreted as water used. Softener turbines don't distinguish direction of flow. That causes the softener to regen earlier than needed. Most of us with softeners with wells figure that is a small factor, and don't have the check valve.

For whatever reason, I think you have a check valve. A thermal expansion tank on such a system should have air precharge set to the highest pressure that the well pump system makes. If you have a 40/60 psi pressure switch, set the air precharge on the thermal expansion tank to 60 or 61. Air precharge on a thermal expansion tank, or for the well system pressure tank, is measured and set while the water pressure is zero.


Ah thank you. I'll pick up a new expansion tank and get that changed out. I'm not shocked its bad because the previous owners of this house appeared to have decided to move rather than fix the issues (mostly minor but many in quantity) that the house had. Which is ok, I do enjoy learning and fixing things. Just had to dismantle my fridge to clear out ice build up in the freezer drain pan that clogged the drain hole

I've never had an expansion tank before on my homes, looks like from researching the process in changing it is fairly simple.

1) turn water heater to pilot setting
2) turn off cold water inlet valve
3) drain about 3 to 4 gallons water from the water heater
4) open a faucet
5) crack open pressure valve
6) remove expansion tank
7) set expansion tank pressure to match the pressure of an outside hose bib
8) turn all stuff back on
 
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Reach4

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I don't think you need all of 3, 4 and 5. I would think #3 might do it after you open a hot faucet.

How about a photo? That might be to check if you could add some additional support.

Draining a few gallons under pressure is normal maintenance to drain any sediment. Opening the thermal expansion valve, draining a bit of water, releasing, and make sure the valve closes is a test you should do maybe annually. That is also done under pressure. So that is not part of the tank changing.

Get a water pressure gauge. The air precharge should be set to about the highest pressure that comes from the city, but measuring just once and adding 2 psi is probably not bad. There is a good chance you will be releasing air, rather than adding. If you know the water pressure in advance, and there will be adding needed, you could add the air at your tire store etc on the trip home. But if you have a tire inflator/compressor, then no problem doing it at home.
Use tape and/or pipe compound.
 

Eliteconcept

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I don't think you need all of 3, 4 and 5. I would think #3 might do it after you open a hot faucet.

How about a photo? That might be to check if you could add some additional support.

Draining a few gallons under pressure is normal maintenance to drain any sediment. Opening the thermal expansion valve, draining a bit of water, releasing, and make sure the valve closes is a test you should do maybe annually. That is also done under pressure. So that is not part of the tank changing.

Get a water pressure gauge. The air precharge should be set to about the highest pressure that comes from the city, but measuring just once and adding 2 psi is probably not bad. There is a good chance you will be releasing air, rather than adding. If you know the water pressure in advance, and there will be adding needed, you could add the air at your tire store etc on the trip home. But if you have a tire inflator/compressor, then no problem doing it at home.
Use tape and/or pipe compound.
 

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Reach4

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I would consider putting a strut (length of copper or pvc pipe or wood) under the copper pipe near the right, to take weight if that tank later fails and gets full of water.
 

Eliteconcept

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I don't think you need all of 3, 4 and 5. I would think #3 might do it after you open a hot faucet.

How about a photo? That might be to check if you could add some additional support.

Draining a few gallons under pressure is normal maintenance to drain any sediment. Opening the thermal expansion valve, draining a bit of water, releasing, and make sure the valve closes is a test you should do maybe annually. That is also done under pressure. So that is not part of the tank changing.

Get a water pressure gauge. The air precharge should be set to about the highest pressure that comes from the city, but measuring just once and adding 2 psi is probably not bad. There is a good chance you will be releasing air, rather than adding. If you know the water pressure in advance, and there will be adding needed, you could add the air at your tire store etc on the trip home. But if you have a tire inflator/compressor, then no problem doing it at home.
Use tape and/or pipe compound.

I would consider putting a strut (length of copper or pvc pipe or wood) under the copper pipe near the right, to take weight if that tank later fails and gets full of water.
I had considered something like that as well. Any concerns i should have in removing the tank from the copper fitting? Just take it easy i assume?
 

jadnashua

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The tank is likely full of water, that may or may not drain fully, so be prepared for it to drain when you try to take it off. Obviously, you want to remove the water pressure so it isn't flowing, but the tank may retain some water. Think holding your finger over the end of a straw...water will be retained in the straw (tank) until the seal is broken. With the inlet water off, and a valve below the tank (probably the WH drain valve, if you press in the air valve on the tank) it might drain, but will be slow.
 

Reach4

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I had considered something like that as well. Any concerns i should have in removing the tank from the copper fitting? Just take it easy i assume?
I have no experience changing a thermal expansion tank. I would think it best to use two big wrenches, not 4- or 5-inch long wrenches.
 

Eliteconcept

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I have no experience changing a thermal expansion tank. I would think it best to use two big wrenches, not 4- or 5-inch long wrenches.
got it removed. Picking up new one later today and will put back on tonight. Thanks for help guys!
 

Reach4

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Pick up a garden hose thread water pressure gauge and a good tire pressure gauge, if you don't have those already.
 

Tuttles Revenge

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The TPR safety valve should also be replaced since its been constantly under stress to the point of opening and weakened.
 

Eliteconcept

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Got it all replaced. Picked up the water pressure gauge. And propped a scrap piece of wood under the pipe for support.
Thanks all
 
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