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Old 25-01-2008, 10:00   #1
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Water heater pressure relief valve necessary ?

Water heater pressure relief valve necessary ?
Yes I am having problems with my Water heater. I now have discovered the pressure relief valve is stuck open.
There are dire warnings about not servicing it properly, but is it necessary on a boat ? The water pressure could never go high because the boat is not connected to town water & the soft boat hoses (verses copper pipe in a house) would leak first even if the small pump could generate much pressure. Does it also protect against high temperature? On 240v the thermostat could fail but the closest outlet is 3m away through plastic pipes is there any significant risk sealing the valve off.
Thanks john
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Old 25-01-2008, 13:08   #2
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Yes.
When water is heated, it expands, and this increase in volume will cause an increase in tank pressure.

The Temperature Pressure Relief Valve (T&P, or TPR valve) relieves this pressure by discharging some liquid.
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Old 25-01-2008, 14:01   #3
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Certainly if you have an electric hot water heater in your fresh water system you need that overpressure relief valve so that you can force the water to go into the bilge (or overboard) should a failure occur in the temperature control else you could steam something valuable (like your skin).
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Old 26-01-2008, 00:53   #4
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Thanks for the replies I will get it replaced.
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Old 26-01-2008, 03:21   #5
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Quote:
Water heater pressure relief valve necessary ?
It could be very important. Look at this news story. The pressure relief valve was plugged. The tank blew through a roof, shot over a six lane highway and landed about 450 feet away.
Four hurt as water heater explodes
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Old 04-02-2008, 21:04   #6
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They did this on

Mythbusters......Expensive way to put a new hole for a hatch in your boat...or a moonpool
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Old 31-03-2008, 19:35   #7
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Interesting thread.
I have another relief valve question: ours lets too much water go: about 1 to 2 liters a day. This started when we started, 2 days ago, to use the electric heating option (never more than 90 mn at a time). Before that, we only had hot water when the engine had been running and didn't even know we had an electric option. The water heater is an Isotemp 40l, was probably installed in 98, we only got the boat in 04 and had been in warm areas most of the time, so hot water was never an issue. Now, we worry about losing too much fresh water. The local rep offers to sell us a new valve for 100 NZD, but all the connections to the tank are more or less corroded (however, they don't leak) and we are afraid to break something more serious if we attempt to replace the valve. Any advice? If we time the electric connection so as never to exceed too high a temp, could we shut off the valve completely? would this be acceptable when we run the engine?
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Old 31-03-2008, 20:55   #8
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As said in the earlier posts you will have an unsafe installation if you remove and plug the relief. I would not even contemplate it.

The problem of the relief valve relieving as the water heats can also be caused if the freshwater pump is one of the multiport ones claimed not to need an accumulator (like this - Accumulator Tank > Pressure System Accessories > Water Pressure Systems > Jabsco - ITT ) in the fresh water system. While the pump may work fine without one, it means that expansion from the hot water heating up in the heater has nowhere to go except out the relief valve - and so it dribbles. So if ones arrangement is accumulatorless and one has such a pump then an accumulator will likely fix the dribble (and also stop the pump cycling briefly when the hot water is allowed to cool and contracts).

The discharge side of the hot water heater relief valve is most sensibly, in my opinion, taken back to the water tank so if the valve does dribble or relieve the water is not lost nor goes into the bilge or wherever. It can just be teed into the tank filler pipe. This seems so blindingly obvious that I am surprised at how few boats are actually done that way.
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Old 31-03-2008, 21:10   #9
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MidLandOne,

You are perfectly right, the common sense would be to return this water to the tank and it should be done at the factory.
Things being what they are, we'll do the next best thing, which is to collect the water in a jerrycan and re-use it.
I just had the same conversation with the same conclusion with the Isotemp rep here in NZ. Furthermore, he says that it is not uncommon for bigger waterheaters (75 l) to "bleed" 1 to 2 liters a day.
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Old 31-03-2008, 21:46   #10
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just run hose from waterheater back to fresh water tank
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Old 01-04-2008, 17:41   #11
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"just run hose from waterheater back to fresh water tank"
Rather than heating up the drinking water (which I usually drink "as is" temperature) I think I'd rather do as Claire mentions and put a jerry can or other containter out to catch the overflow. Possibly even a 2-liter thermos bottle, so the scalding water can be used almost-ready for cooking or the kettle. Why waste it in the main tank?!
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Old 01-04-2008, 19:29   #12
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Actually, cos it is only an occasional dribble, the water is almost instantly cooled to just lukewarm the moment it gets through the valve and has travelled a few feet in the cool pipework.

Assuming it isn't going like a hosepipe, in which case one would assume there was something major that needed rapid fixing .
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Old 02-04-2008, 08:40   #13
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Just so I understand correctly - Are you talking about the valve, in the top right of the water heater in the link below 9with the yellow tag on it?

Water Heater

The reason I am asking, is that these water heaters also have another "protection" valve (the longer valve, top left), which i believe protects against sending water to the hot water tap - that is too hot - to prevent scalding!
A friend of mine replaced a defective, older, higher end water heater with the one pictured, and could not ge tthe water hot enough. he had to remove the anti-scalding unit, and then it worked fine. he says it still doesn't keep the water hot, for nearly as long, as his old heater.
the older models of this same unit did not have this anti-scald (forget the proper term) valve!
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Old 02-04-2008, 13:41   #14
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Anti-scald valves have become a commonly available item in the last decade. I wasn't aware that water heaters were shipping with them, that sounds like some maker got sued (or scared) and started putting them in despite the fact that "at the heater" is the wrong place for them. They need to be at the faucet end of things.

(Kinda like forks and toilet paper, each works best at the right end of things, and not too well at the other end.<G>)
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Old 03-04-2008, 03:39   #15
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From the Kuma (Force 10) Hot Water Heater instructions:
“... If your unit is equipped with a TCV (Temperature Compensation Valve) the
coolant loop to the water heater exchanger must be an auxiliary loop in the engine coolant circulation system. The TCV can not be installed inline with the engine coolant system. Figure 1 on page 5 ...”


Goto: http://www.kuumaproducts.com/Eng0092...s%20Manual.pdf


Many building codes have been amended to specify that new or replacement water heaters supply a maximum hot water temperature of 49 degrees Celsius (120 degrees Fahrenheit).
It’s recommended that you add an anti-scald mixing valve* on the Hot Water Tank,
OR
thermostatic mixing valves** (or pressure-balanced valves***) on each hot water tap and showerhead.

* Anti-scald mixing valve: This valve is installed directly into your plumbing system (at the hot water tank), and it mixes hot water with cold water to ensure the water that comes out of the mixing valve is not above 49 degrees Celsius (120 degrees Fahrenheit).
This is the “Temperature Compensation Valve” noted on the Force 10 heater.

** Thermostatic valves: These valves operates in the same way as an anti-scald mixing valve in your plumbing system. The difference is that a thermostatic valve is installed at select points of use (hot water taps and showerheads).

*** Pressure-Balanced mixing valves: A pressure-balanced (shower) valve is designed to compensate for changes in water pressure. It has a special diaphragm (or piston mechanism) inside, that moves with a change in water pressure to immediately balance the pressure of the hot- and cold-water inputs. These valves keep water temperature constant, within plus or minus 2 to 3 degrees Fahrenheit, but do so by reducing water flow through either the hot or cold supply. Most reduce water flow to a trickle if the cold water supply fails.

Flow can be a problem with pressure-balanced valves, particularly in homes where the shower includes a personal hand shower and/or a multiple-head shower system. Most pressure-balanced valves are either full-on or full-off.

Where flow and volume control are important, a better (and more expensive) choice is a thermostatic valve**. Most of these have 3/4-inch inlets that can blast a flood of water through multiple showerheads and will maintain the water temperature within 1 or 2 degrees of the set temperature.

Whereas a pressure-balanced valve will typically cost from a low of $100 to $250, a thermostatic valve with a volume control (a separate feature with most), will run from $400 to $1,000 depending on the features and trim.
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