ArrrrrgH! (H.W. TP relief valve)

[kloudie1]

I partially agree with your rant, Maine.. but I have been in a situation where, by opening the hot faucets fully, I was able to get the screaming high temp alarm on the engine to stop while I got out the way of a tow on the Intercoastal.. I am not sure that a tempered heater would have done that. The real problem was a plugged elbow water outlet, but I was able to get out of a problem that way.. (ok, boat was newer and I didn’t know about elbows plugging etc.. but I did know that the cool water in the heater would help.. )
You are correct of course about the rating mismatch, but I am surprised that there have been no reports (that I am aware of) of failures in the hot water piping.. If someone were to insulate it and let the tubing get really hot… there would most likely be a problem..
I know that my TP valve drools slightly when on electricity and is started up from cold. A small accumulator on the hot side to accept the expansion volume would probably stop that.. I never have really wanted to fiddle with it since the tank is 25 years old.. and I know I am living on borrowed time!

 

[Roger Long]

Boy, do I feel stupid. I don't think I've ever wasted so much of forum readers time on a non-issue.

By casting off the hangers, I was able to get enough slack to get a pipe wrench behind the hose and turn the TP valve. I then hacksawed away some of the piping and the valve stem cleared the frozen nipple by a hair. The interference was an optical illusion caused by peering through all the hoses. A couple hours later and it was all back together and working perfectly.

Thanks for the offer of the tools MaineSail, I have all that stuff but I didn't think I could swing them in the space.

I went down to Maine Hardware to buy the 75 psi TP valve I looked at when I was considering making my bulkhead tank pressurized. It was gone. They made some calls and were told by one supplier that the 75 psi units have been taken off the market and are no longer available. Probably too many lawsuits from flooded basements. Maybe this is wrong but I needed a valve right now.

Since the whole system is piped up with hose and there is no way to hard connect it to street service pressure, I decided there was no harm in using a standard 150 psi valve.
Only temperature expansion could create pressure above the 12 volt pressure pump setting. As you pointed out above, all those hoses and hose clamps are going to start spouting water somewhere long before the system get much above 75 psi. The temperature setting of the new valve is the same as the old and that's what's really critical.

I put the obstructing piping in with Sharkbite fittings this time so I can replace the TP valve easily the next time it goes flaky.

 

[Bill Roosa]

Pressure in a hot water tank

If you use the hot water occasionally then the only pressure would be from the pump and a smidgin from the cold replacement water heating up and expanding.
FWIW

 

[kloudie1]

That is good news, Roger. Glad the thing came off without a fight !

 

[RAD]

Glad you did post this because I learned something

 

[thereisabelle]

I am happy your situation is favorably resolved! I lost a good twenty minutes of hunt and peck going back and forth to re-read your arrrrrgh! hit the wrong key and poof! but never fear i will tackle the water heater on the 73 irwin someday.... i can barley reach it to touch with my fingertip from the aft head. can't even see it from engine room or salon.but i can count on you guy's right! jimbob

 

[Scott B]

If you need pipe wrenches and pipe dope I can drop this stuff off this affternoon...

That would be great, I'll send you directions via PM......