hot water tank overflowing

[gettinthere]

I've had the boat for 6 years and never had this problem until now.
We're on a mooring and go to the dock about every two weeks for water. The last two times, after filling the tanks, I see the bilge pump putting out water. Looking below, I find the overflow of the hot water tank dumping water into the bilge.

Two maybes. One is that the overflow pressure relief valve has weakened recently. The other is that twice in a row we have emptied the hot water tank and it started some kind of vacuum by getting overheated from the engine heating circuit.

We've motored 24 hours straight and the engine heat wasnt enough to cause this in the past. The trip to the fuel dock is maybe 15 minutes each way.

I'm not sure if my second idea is even possible.
The first idea, the pressure relief valve; can and do they go bad? Anyway to verify its the problem? Easy replacement part?

Thnx

 

[Stu Jackson]

Once those pressure relief valves pop once they often get fouled with whatever may be in the water and stay open.

They are an easy replacement from any hardware store. Just check the label and see what it is rated for.

If there's no label, find a Seaward or Kuuma or Raritan heater manual spec and replace in kind.

 

[Ralph Johnstone]

One is that the overflow pressure relief valve has weakened recently.

Maybe you're putting too much water into the hot water tank :Liar:.

But seriously ................ everything that Stu says but take a quick look here before putting your money down and tearing the skin off your knuckles.


http://forums.hunter.sailboatowners.com/showthread.php?p=1179938&highlight=relief valve

 

[Bill Roosa]

are you sure it is coming from the hot water tank? Since it only happens after topping off the fresh water tanks could it be a fresh water tank vent leaking into the boat?

 

[Capt jgw]

The T&P valve should open at upwards of 180 deg. If your engines not overheating, the valve shouldn't be leaking. I wouldn't worry about the rating of the valve, I think they're all the same. Thread size might be an issue though. I changed one on an Attwood heater, it was 1/2" and all the hardware store had was 3/4". Had to buy a pipe adapter to make it fit.
Check out the Mythbusters episodes on water heaters. Some of the most spectacular explosions they did were water heaters with capped T&P valves.

 

[gettinthere]

OK, I'll change the relief valve.

I can see the water flowing directly out of the hot water tank overflow and it's hot water. 100% positive it is not from anywhere else.

 

[bmoller]

When my tank was leaking it was the heating element. I found one at a camper supply house

 

[kloudie1]

It is the transition from cold -to-hot that is doing that.. When ya turn on the pressure pump, everything is cold so the tank gets pressurized cold.. Then the engine heat starts warming it and the water expands and has no place to go since the pump discharge valve is closed and the faucet is closed.. the pressure builds up until it pops the pressure relief valve which may or may not re-seat.. They normally will re-seat. Couple of things that you can do to stop it.. 1; briefly open the hot faucet after running the engine for 5 minutes or so.. or 2, you can install an accumulator in the pump discharge line to absorb the pressure and keep it below the pop pressure. Yes, the Temperature/Pressure Relief valve can go bad and can be fairly easily replaced ..but generally a new one will drool a little under the warm-up unless there is an air bubble in the tank or an accumulator or someone opens the faucet and bleeds off a half cup of water or so. I open the faucet when warming up.

 

[Claude L.-Auger]

Klaudie gives you a good trick in opening the faucet. Turn off the pump breaker otherwise your pump will turn on and keep on refill the tank. When I re-commission the boat in the Spring, I open and shut the pressure relief valve a few times until it reseats properly. I have attached a hose to it going to the bilge. Never have lost more than 1/2 a cup when turning on electric element or starting engine.