Home>Discussions>PLUMBING>New Expansion Tank/T&P Valve Still Leaking
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Gray Watson
Re: New Expansion Tank/T&P Valve Still Leaking

Some vacuum breakers also function as backflow preventors do you have the wrong vacuum breaker installed or no vacuum breaker installed? Some braided hoses have checks built in, example watts floodsafe connectors.

Someone handy with a meter can check for voltages on your elements to determine if the thermostats are working, making sure those elements aren't scaled over, loose, or rust inhibiting full contact to the tank, and that the high limit is functioning properly. Also make sure your circuit protection is correct for the water heater (some DIYers will swap out a larger CB or put a penny in the fuse socket to counteract the annoying tripping caused when a high limit has been jumped due to its annoying habit of opening and having to be reset, or isn't working at all in the first place).

You can check pressure from the drain bib on the water heater.

Re: New Expansion Tank/T&P Valve Still Leaking

I'll second that, Goldhiller. Checks in the nipples. Good observation. You get the attaboy for the day.:cool: Could still be the T&P I've heard of it happening. Where'd it come from someone could have cleaned it up and returned it used, You don't know.

Re: New Expansion Tank/T&P Valve Still Leaking


If this hasn't been mentioned by now....it should be pretty easy to determine if the PRV is at fault here.

Open a faucet and run some water to stabilize the pressure at 40 psi. Might just as well do this at a hot water faucet and draw enough water that the WH is sure to kick in. Then close the valve on the main house supply so that no more water can enter the system anywhere (WH or the cold water lines). Hopefully you have such a valve upstream of your new expansion tank AND it closes dead tight cause any introduction of water into the system will skew this test...rendering it worthless. Likely you have one just upstream of the PRV which allows you to service that if/when it needs it. Then wait and see what happens.

If the T&P doesn't drip/pressure doesn't build to excess...this should be confirmation that 1- you don't have a runaway heating element and 2- that the expansion tank is doing the job it's designed for.

If all is well at the end of that little test...open the main supply valve again and see if the pressure builds. If it does...you gotta faulty PRV. I suspect that this what you will discover....but I've been wrong before. Just once to the best of my memory.

Re: New Expansion Tank/T&P Valve Still Leaking

Thanks goldhiller - good diagnostics!

The pressure only rose in the system after several hours, so I didn't see it initially. I turned the water heater and the cold supply to it off and left it off all night, then checked the pressure gauge in the morning - over 200 psi (the gauge stopped reading at 200)! I replaced the PRV, and all is well so far at 50 psi - no leaking, expansion tank empty, etc.

Thanks for all the replies!

Re: New Expansion Tank/T&P Valve Still Leaking

Good stuff and thanks for the reply.:)

Fred Lesto
Upgrading heating system in 1927 Tudor home

We are planning to up grade our heat & hot water systems. We have picked a Weil Mclain Ultra #3 155btu modulating boiler with an indirect water heater of 40gal. We have cast iron radiators and the boiler has an alumimun heat exchanger will there be an electrolisis problem with this?:confused: Should we go with a tankless water heater what are the PROS & CONS on this before I make this expensive discision all help will be apprieciated.:D


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