Drainback System Hot Water Heater leaking

[erobinson32]

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[Amy@altE]

Are you sure it is just a pressure relief valve and not a temperature and pressure relief (T&P) valve? I've had installers accidentally install a T&P valve, and every time it got hot, it blew, as it is supposed to. Make sure it is just pressure, not temp.

Which tank is the valve on, the hot water tank or the drainback tank?

[J.P.M.]

Do you have an expansion tank on the house (pressurized) side ?

[Amy@altE]

Do you have an expansion tank on the house (pressurized) side ?

Oh, good call. My town has a check valve on the water input, so when I had my 4 collector system cranking, my T&P valve went off on my hot water tank. A big expansion tank fixed that.

[erobinson32]

Are you sure it is just a pressure relief valve and not a temperature and pressure relief (T&P) valve? I've had installers accidentally install a T&P valve, and every time it got hot, it blew, as it is supposed to. Make sure it is just pressure, not temp.

Which tank is the valve on, the hot water tank or the drainback tank?

[removed]

[erobinson32]

Do you have an expansion tank on the house (pressurized) side ?

[removed]

[J.P.M.]

Oh, good call. My town has a check valve on the water input, so when I had my 4 collector system cranking, my T&P valve went off on my hot water tank. A big expansion tank fixed that.

Supplier check valves at residential inlet are common.

When water heats up, it expands. So does most everything else, but the net effect is usually that the contained H2O vol. increases more than the system vol. wants to (increase). Water being mostly incompressible, the system vol. will increase to match the water vol. The result is an increase in system pressure, and one of the more common causes of reduced water tank life. Properly sized and maintained expansion tanks are usually a part of any well designed DHW system.

Add: a relief valve is there for safety. It will operate at or hopefully before the tank design pressure is exceeded or probably at/before +212 deg. F. The expansion tank is part of good system design and to help keep system pressure within a reasonable operating range and prolong system life.

[J.P.M.]

We do not have an expansion tank on the house. The house was build in 2008, so I'm surprised we do not.

Don't be surprised. Most contractors are either unaware of the need or ignore the need if not mandated by local code.

[erobinson32]

Don't be surprised. Most contractors are either unaware of the need or ignore the need if not mandated by local code.

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[Amy@altE]

So it's the valve on the water heater itself? Then yes, it should be T&P. If it was on the drainback tank, then it should be P only.

It should be really quick for a plumber to install an expansion tank, shouldn't be unreasonable cost. JPM, what size expansion tank do you recommend? I know I really oversized mine, I got such a varied range of opinions, I decided to err on the big side. (I've been out of thermal for a while, I'm rusty, should have caught that it was the expansion tank.)

[erobinson32]

So it's the valve on the water heater itself? Then yes, it should be T&P. If it was on the drainback tank, then it should be P only.

It should be really quick for a plumber to install an expansion tank, shouldn't be unreasonable cost. JPM, what size expansion tank do you recommend? I know I really oversized mine, I got such a varied range of opinions, I decided to err on the big side. (I've been out of thermal for a while, I'm rusty, should have caught that it was the expansion tank.)

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[J.P.M.]

So it's the valve on the water heater itself? Then yes, it should be T&P. If it was on the drainback tank, then it should be P only.

It should be really quick for a plumber to install an expansion tank, shouldn't be unreasonable cost. JPM, what size expansion tank do you recommend? I know I really oversized mine, I got such a varied range of opinions, I decided to err on the big side. (I've been out of thermal for a while, I'm rusty, should have caught that it was the expansion tank.)

It varies with the size of the plumbing system including the tank, system pressure and the lowest design pressure of all the component design pressures in the system plus elevation head. Big system w/low design pressures --->>> bigger expansion tank.

Watts/others have expansion tank sizing sizing methods on the net. My water sys. is about average size, the expan. tank's about 3gal w/bladder. Cost was about $40 or so, a globe valve for servicing and a pressure gage to keep an eye on things. Took ~~1-2 hrs. to cut some copper & sweat a few joints.


Suggest you try this: Get a pressure gage from big box and put it on the H2O tank drain and observe the pressure. Can't hurt.

[LucMan]

Do you have a well, or city water?
What is the inlet water pressure to the house?
What are the pressure & temp that the T&P valve is rated for?
How old is the system?

[peakbagger]

One important thing is that you need an expansion tank rated for potable water use. It has to be lined with a non corrosive material. Standard heating type expansion tanks are generally mild steel that work fine for closed loop heating as the oxygen rapidly is depleted, but on a potable water system there is always new oxygen and other potential corrosives to be introduced. A standard tank will work but will not last as long. Its very dependent on the local water how long it will last.

I have seen a few tanks on hot water systems retrofit over the years by removing the relief valve and installing a tee fitting then hanging the tank off the branch of the tee. The tank should have the connection on top and the Schrader valve on the bottom so a length of straight pipe, elbow and thread nipple is needed on most hot water tanks, so the tank can be oriented correctly. The tank can go anywhere unless there is a circulating pump on the hot water system. This is rare on residences but more popular on commercial. If there is a circulating pump, the tank goes upstream of the pump suction. The expansion tank pressure needs to be adjusted to the houses working pressure. They usually come precharged at 15 psi which is too low for most residential water pressure. I need to look up the formula for the charge pressure but I believe its the maximum incoming water pressure plus 5 psi. The pressure has to be set at least 5 psi below the safety relief valves setting. If you incoming pressure it too high, you may need to reduce it. Adjusting the pressure requires a tire gauge and a bicycle pump.

[LucMan]

Use an Extrol ST-5 this is adequate for a 80 gallon solar hw tank, if needed.