Quote:
Originally Posted by MudDog
This reminds me of an issue I had at home.
Our city water meter does not have a back-flow valve (new meters are required to, but the older ones don't have it).
6-7 years ago I installed a security system and decided to buy a WaterCop water valve. I programmed it so when I arm my security system "away" the water to my house is shut off and when I disarm "home" it turns the water to my house back on. I don't have to worry about leaks or burst pipes when I'm away. Outside sprinklers are before the valve, so outside still gets water.
Anyway, shortly after installing I started getting drips from the pressure relief on the hot water heater. The water cop valve was preventing back-flow as the water/air in the hot water heater tank expanded and it had no where to go so the pressure relief did it's job. I ended up buying a small hot water heater expansion tank so the pressure had a place to go and that solved the problem.
In your case it's intertesting that the fittings hold pressure when running cold water thru, but can't seem to hold the pressure when the hot water heater water is expanding. Also interesting that the fittings are failing before the hot water heater pressure relief valve.
A few years ago, I installed a Shurflu accumulator tank on my TM to quiet and minimize the water pump when dry camping. It's installed after the pump. The pump has a back-flow valve.....so when there's expansion from the hot water heater it is pushing back and hitting that back-flow valve and everywhere else in the loop finding the weakest point to relieve the pressure.
Assuming there is not something wrong with the hot water heater (i.e. run-away thermostat, etc), I wonder if installing an accumlator tank would give the pressure a place to go (like an expansion tank for a household hot water heater)? The accumator tank would be in the loop whether running on pump or city water.
Searching the internet for differences between accumulator tanks and expansions tanks gives conflicting answers....
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In searching more I have found several references to rv leaks only when the hot water heater is on.
I would say:
1) reset the air pocket in the hot water heater (see link below)
2) replace the pressure relief valve with a properly set replacement and reset air pocket
3) try installing an accumulator/expansion tank if you still get leaks when hot water heater is on.
The PEX is holding the pressure of city water when the hot water heater is off, correct? So it's only when you are getting expansion from the HW Heater. If you fix one connection, it's just going to find the next weakest one to leak from. Eventually it may get to the pressure relief valve (where it should) but by then you may have replaced every connection in the TM.
I believe the PSI on the accumator tank is normally much less than the city water PSI or the pressure require to trip the hw heater pressure relief valve...so if it holds city water pressure, it should be able to expand into the accumlator tank when needed.
If you dry camp, it's a nice add-on anyway to keep the pump cycling down.
Here's a few threads I found:
http://www.outbackers.com/forums/ind...?showtopic=660
Here's how to reset the air pocket that is supposed to be in the hot water heater to allow for expansion:
http://www.rv-motorhome-answers.com/...r-heaters.html
and a couple more links discussing expansion tanks:
http://www.marxrv.com/plumbing/plumb.htm
http://www.marxrv.com/hints.htm#expansion