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Old 11-11-2015, 13:57   #1
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Hot Water Tank Pressure Relief Valve

My hot water tank's pressure relief valve is leaking. At least I think that's what it it. It's the red thing in the upper right corner of the picture.



The boat is a 2005 Southerly 110. I've reached out to the Northshore, but I've yet to hear anything back.

Any thought, or suggestions on what / how I should replace it?
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Old 11-11-2015, 13:59   #2
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Re: Hot Water Tank Pressure Relief Valve

Until I saw it I was going to say it's just a T&P valve, go to the home improvement store and pick one up, but that one looks different.
T&P of course means temperature and pressure, exceed either's set point and it opens up keeping the water heater from literally exploding
A normal one just screws in very easy to replace, that one you have I don't know about though, I'm not suggesting you replace it with one from a box store
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Old 11-11-2015, 15:00   #3
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Re: Hot Water Tank Pressure Relief Valve

So what happens is when the system is pressurized it leaks. I can twist the knob several times and it seems to re-seat itself. Each time I twist it water shoots out.

Alternatively, I just leave the fresh water pump off until I need it and it doesn't leak.... But I'm a bit forgetful.
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Old 11-11-2015, 15:56   #4
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Re: Hot Water Tank Pressure Relief Valve

Take it off, and see if you can service(clean)it! Also note, that if you have to replace it, make sure you get the same length probe! That's the plastic pencil like part that sticks into the tank. Also the same temp rating. The temp rating on my tank probe, was/is lower than household! I can tell you that when it fails, it will it will fill you bilge. Ask me how I know that !!!!!! if you leave the pump on. Ours, pumped about 70 gals into the bilge. 180 degree water, on the bright side did help clean the bilge partially from the motion of the boat!
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Old 11-11-2015, 19:23   #5
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Re: Hot Water Tank Pressure Relief Valve

Quote:
Originally Posted by mike d. View Post
Ours, pumped about 70 gals into the bilge.
Well... I know!!! 60 gallons and a faulty fresh water tank sensor. It wasn't until I went to "sleep" and heard the drip-drip-drip that I realized I wasn't obnoxiously using water, but I had a leak!
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Old 12-11-2015, 08:53   #6
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Re: Hot Water Tank Pressure Relief Valve

It's important to change with same pressure relief rating, one would not want a BLEVE (Boiling Liquid Expanding Vapor Explosion) situation as Myth Busters shows what can happen. Hell of a bomb!
Might also want to check if there's a sacrificial anode needs replacing, usually but not always on the hot side looks like a pipe nipple.
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Old 12-11-2015, 08:54   #7
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Re: Hot Water Tank Pressure Relief Valve

Pressure relief valves are not really intended to be service. If you talk to the manufacture reps, they will say they are good for one shot. That does not mean they will never stop leaking if they pop off once. It just means that if they do seal, you're ahead of the game. But it also means that once they pop off, replace it. Cheap actually.

When mine failed I bought a new one at the home improvement store for $12. A dock mate spent $72 for the exact same one at West Marine. When I told him, he gave himself comfort by saying that he felt assure that his was "marine grade".

But in all honesty, that does not look like any PRV I have ever seen. They are generally non adjustable. Nonetheless, I would pickup a Watts PRV and be done with it.
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Old 12-11-2015, 09:01   #8
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Re: Hot Water Tank Pressure Relief Valve

Before you ting apart try the following:
Water heaters need some air cushion inside to allow for the expanding hot water. Mostly that happens naturally when you fill them, but after a while that air bubble gets absorbed and goes away and with out it the expanding water causes the pressure valve to drip a bit.
Try this - Drain the hot water tank down about 1/2 way by turning off your pressure pump, opening the drain , and then opening the over-pressure valve to allow the water to drain and air to enter. Close the over pressure valve, turn on your pressure system and let the system refill.
Check it again after the system is hot and used a few times - it may just cure the problem this easy way.
More over pressure valves are sold because people do not know this than those actually needed.
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Old 12-11-2015, 09:10   #9
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Re: Hot Water Tank Pressure Relief Valve

Yours appears to be a UVGold unvented T&P valve made in the UK.
https://www.mrcentralheating.co.uk/t...e#.VkS5YV877v4
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Old 12-11-2015, 09:32   #10
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Re: Hot Water Tank Pressure Relief Valve

Quote:
Originally Posted by seasick View Post
Yours appears to be a UVGold unvented T&P valve made in the UK.
https://www.mrcentralheating.co.uk/t...e#.VkS5YV877v4
This brings up a good point. UK T&P's relief at a lower pressure then a USA T&P relief. This as the tank construction and pressure ratings are different. I would not put a US T&P relief on a UK clorifier. They are not built to the same code. Use a UK T&P relief on a UK water heater. The pressure relief rating of the US T&P at 125 psig, is too high and the UK tank might fail first.
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Old 12-11-2015, 10:59   #11
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Re: Hot Water Tank Pressure Relief Valve

I would pull it out and apart. Looks as if there is a packing glad? An O-ring or something locally available might solve the problem.
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Old 12-11-2015, 13:05   #12
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Re: Hot Water Tank Pressure Relief Valve

I replaced my TPV (temperature and pressure valve, 180F and 2.5 bar) for an IsoTemp water heater on my European built Jeanneau. I note in your photo that the relief valve says 'made in Italy' meaning it almost certainly has metric threads. In my case, the valve has BST (British Standard Thread), so no sourcing from a home center ... which is a bad idea IMHO ... be sure to get a valve that both protects against excessive pressure and temperature. I had to order mine from the UK, even though it is a Honeywell valve ... US customer service was non-existent.

Good explanation Sailorchic34 !!
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