Hot water tank

[Russell]

Has anyone had a problem with the pressure relief valve on their hot water tank? If the pressure water pump is on when running the engine the valve opens after the water gets hot and lets out the hot water inside the bilge. Turning off the pressure pump stops it but we need to use the fresh water shower at the stern while fishing. I put a wrench on the valve but it did not turn readily and I am afraid of cracking the 10 year old tank trying to get it loose. Any reason not to cap it off? Is there any way to adjust it?

[jleonard]

Sounds like you need a new valve. I never met one that I couldn't get off with a big enough wrench...or with a pipe for leverage.
You don't want to plug it off...pressure relief valve...the name says it all.

[chiefrcd]

The pressure vessel explosion of a 30 gallon hot water tank can literally tear a house in half....seen it with my on two eyes...not sure what a six gallon tank would do but I would not take any chances with it.

[Russell]

Turned out that replacing the pressure-relief valve was easier than I thought. A big pipe wrench turned the old one and the tank stayed in one piece. And since I got the replacement at a hardware store for $11.00 it was one of the cheapest repairs I have made. But I have been thinking about the necessity of these valves. Unless I use the shore power electric heater the water can never get hotter than the engine coolant and the only pressure comes from the little water pump. I don't think that little pump could ever generate enough pressure to rupture the tank. And on a home unit where the possibility exists that the gas or electric heat stays on and boils the water, why does it not go back into the feed pipe? Is there a one-way valve on the incoming cold water line? If not the pressure should never get higher than the water pressure.

[DougSea]

Hey Russell,

Here's a link to some T&P info: http://www.plumbingpages.com/featurepages/HWT&P.cfm

I don't know about your boat but on mine, when running hard, the temp gets up there. Being a pressurized, anti-freeze filled system temps above the boiling point of regular water are certainly possible. I know that my "engine heated" water is MUCH hotter than my "Heating Element heated" water. And what if the electric element WAS on and malfunctioned?

In either case, you add an inlet check-valve (to prevent hot water from backing out into the cold) and you have a potential closed, superheated system - and the chance of a bomb going off under your helm seat!

Note that in a home system a back flow preventer and/or a pressure regulator both would turn your overall water system into a closed one.

Glad to hear you got that replaced without much grief!