mystery leak

I didn't know that. Thanks for correcting me. They sound like a great fitting to use in tight places. Robert

I had some time last weekend to work on the mystery leak some more. I confirmed that the leak occurs even when not hooked up to shore water (i.e. just the fresh tank and the pump.) Basically I’m getting leaks anytime the hot water heater runs, electric or gas, shore water or pump. In thinking about this, it makes sense given the anti-backflow valve on the shore water intake. Basically it’s a closed system inside the TM.

Additionally, I did a better job of capping off the hot and cold supplies to the external shower. These were the original leak spots. After doing this, I started to get leaks in three places: The hot water output from the hot water tank, the hot water supply to the internal shower, and where the fresh water leaves the pump. These leaks are worse than what I was seeing before at the ext shower. The leaking is also more pervasive when a full tank of cold water is being heated vs just an incremental heating cycle to reheat after using maybe a gallon or so of hot water.

The hot water heater manual claims the t/p valve should release at 210 degree or 150 psi. Both of these seem crazy high. I have never seen the t/p valve release on its own – and I had some time to kill and watched it. I measured the water temp and it was ~135 degrees. I haven’t measured the pressure at the hot water heater output yet – need some adapters - but I might for grins. 100 psi breaks ¾” pvc lawn irrigation. I would imagine 150 psi would blow apart the TM PEX plumbing. I did pull the lever on the t/p valve and allowed water to flow through it so I’m sure it’s not outright clogged. This did not change the leak behavior. I also tried the suggestion in the manual to make sure there is an air pocket in the tank. That made no difference – or maybe made it leak a little bit more.

Immediately after a full hot water heating cycle (leaks had started up), I turned on the hot faucet in the kitchen sink and could hear the pressure release from the tank. It’s not like it was spitting air out of the lines, but the pressure release was noticeable as I have the TM pretty much empty and the cabinet doors open. Cleary the hot water heater is generating more pressure than the TM PEX plumbing can handle.

It seems to me that one of maybe 4 things is happening here:

1) The t/p valve is somehow faulty and should, as normal operation, always weep or otherwise let off pressure every time the tank heats up. My impression from reading the manual is this shouldn’t really be the case. Has anyone noticed otherwise?

2) The t/p valve is not really relevant given its high limits and somehow the hot water heater took a turn for the worse and creates pressure above what the PEX system can deal with but below the t/p trip point. Need to have the hot water heater replaced.

3) I’ve had this leak (at the ext shower) from day 1, never noticed it, and the assembly of my TM was poor. This is possible given our TM is only 2.5 yrs old and our use model. All leaks are happening on ½” pipe threaded connections. At least on the outside shower, there was no teflon tape nor pipe dope. Does anyone know if these are typically applied to the PEX connections w/in a TM? I used Teflon tape to improve the temporary cap at the ext shower and that started the Pillsbury Dough Boy affect.

4) The system is designed to leak at the ext shower, the low point in the system – but not really designed as a drain. This is rot waiting to happen.

Thoughts?

(I hate plumbing! Electrical systems are much more deterministic )

The T/P valve is a safety device and should never operate during normal operation. It certainly sounds as if you have isolated to problem correctly to be the expansion of the water in what is temporarily a closed system. It does seem strange though that the pressure in a 6 gal water heater would increase that much to cause a leak especially when the original pressure was limited to what the 12V water pump left the system.
According to the 1993 BOCA Commentary (P1508.7) and the 1997 International Plumbing Code Commentary (607.3), 40 gal. of water heated from 45°F to 145°F will have 1 gal. of thermal expansion, a ratio of 40:1 or in the case of the TM 6 Gal tank. 0.15 gal expansion. Sounds like the PEX crimp tool was not calibrated correctly that day. If you can borrow a crimper, you might try re-crimping before you redo the system.

[Bill]

Releasing system pressure via the t/p valve did not change the leak behavior? Wow. OK, I admit I'm stumped. My only conclusion is that the joints were assembled poorly, and need to be re-assembled.

As for your four questions, I can only tell you that the answer to number 4 ("intended to leak at the shower") is an emphatic NO.

I'm a little confused about threaded connections in a PEX system. I'm no plumber, but I'm not aware that PEX tubing itself is ever threaded. PEX tubing can be connected either by crimping onto a brass fitting (the other end of which may be threaded), or with plastic compression fittings (which screw together). Is it one of these that is leaking? Is it leaking at the PEX tubing, or at the point where the fitting's threads engage the mating threads in the water heater, shower valve, or whatever? The point I'm ambling around to is that plastic or brass threaded fittings for PVC (and perhaps PEX) should have teflon tape on the threads, whereas crimped or compression fittings (I believe) are not taped.

Bill

Frustrating problem, I had a leak at the hot water tank where the threaded fitting went into the tank, it took me 2 tries to get it fixed. Also, if i remember correctly PEX is rated at a really high pressure, I'm thinking I read something like 400 psi. so that would indicate what was said above, you have poor connections. If it were me, I would redo all of the leaking connections using the brass PEX fittings (not crimped) where ever possible.
Good Luck....

[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....

Originally Posted by Bill

Releasing system pressure via the t/p valve did not change the leak behavior? Wow. OK, I admit I'm stumped. My only conclusion is that the joints were assembled poorly, and need to be re-assembled.

As for your four questions, I can only tell you that the answer to number 4 ("intended to leak at the shower") is an emphatic NO.

I'm a little confused about threaded connections in a PEX system. I'm no plumber, but I'm not aware that PEX tubing itself is ever threaded. PEX tubing can be connected either by crimping onto a brass fitting (the other end of which may be threaded), or with plastic compression fittings (which screw together). Is it one of these that is leaking? Is it leaking at the PEX tubing, or at the point where the fitting's threads engage the mating threads in the water heater, shower valve, or whatever? The point I'm ambling around to is that plastic or brass threaded fittings for PVC (and perhaps PEX) should have teflon tape on the threads, whereas crimped or compression fittings (I believe) are not taped.

Bill

I have not seen leaks at the crimped connections. All the places I've noted leaks are as Bill described: "at the point where the fitting's threads engage the mating threads in the water heater, shower valve, or whatever".

I've only undone two of those conenctions, the ones at the external shower, and there was no teflon tape. I guess the next thing I'll try is to put some tape on those and see how that works. Getting to some of these is going to be difficult. It might be easier to smear some pipe sealant / pipe dope on the threads. Does anyone know if there are any issues using that stuff on plastic threads and/or if it's any more or less effective that teflon tape? Thx

My experience was that the pipe sealant worked better than teflon tape on the threads, and be sure and replace the threaded part with a new part, don't try and use the old one. Which I suspect you have done. Hope that helps.

Several of the PEX threaded fittings use a cone shaped washer inside of it, such as the connections on my shower. The washer is what stops the leaks when properly tightened and not cross threaded. The threads have no job in making the connection leak proof other than tightening the washer to the 2 sides. By the way, I cannot find a source for these washers other than a new fitting. Ten cent part that will cost you $10.

Dave, I found those washers at ACE hardware. I'm not sure if all ACE stores carry them, but the one in South Fork Colorado does.