Kuuma Water Heater Leak

[dkinzer]

I went out to our boat last week to do some end-of-the-season prep and, as usual, I turned on the breakers for the cabin lights and the water pump. The water pump ran briefly, perhaps two or three seconds, and then shut off. I had noticed this behavior for several months but I didn't think much about it. I figured that one of the faucets had drained off the pressure during our absence.

While I was out on the foredeck, I noticed that the bilge pump was discharging for several seconds, shutting off and then repeating the discharge. I went below to check the bilge and heard the water pump running continuously indicating a plumbing leak rather than a hull leak. I shut the water pump off and started investigating. The first place I looked was the water heater and, sure enough, the pan below the heater had water in it and when I turned the water pump back on I could hear water running inside the heater.

I pulled the water heater out and took it home where I removed the aluminum surround and found a hole in the tank (first photo).



I was able to find the same Kuuma 11841 heater at Defender Marine for a good price including free shipping - it will be arriving later this week. The same model is also available on Amazon at a slightly higher price.

I was interested to know what the internals of the water heater look like so I cut out a panel using an abrasive disc (second photo). The larger diameter tube is the heat exchanger. The total length of that tube is about 68 inches so if the internal diameter is 5/8" that would indicate a capacity of about 12 fluid ounces (about 0.35 liters).



The third photo shows the leak from the inside on the panel I removed.



I am in the process of re-configuring our Webasto diesel heater to that we can switch between having the engine heat the domestic water and having the Webasto heat it. The significance of that is that I was going to have to partially drain the antifreeze out of the water heater and the hoses between it and the engine so the timing of this failure was fortuitous.

 

[jssailem]

Great report.
Not many have had a chance to see the insides of the water heater.

I have not had many times when hot water was an issue. The water heater I purchased 10 years ago came well insulated. The water stays hot for about 36 hours. I am not taking long hot showers so consumption is minimal. I can see if you consume large volumes of hot water at anchor, your Webasto system will help to maintain the comfort on board.

 

[Ralph Johnstone]

The significance of that is that I was going to have to partially drain the antifreeze out of the water heater and the hoses between it and the engine so the timing of this failure was fortuitous.

You can't knock it but every so often, and it's not very often, you do get lucky.

I've got to say, that corrosion perforation looks more like a drive by shooting. Any idea what's causing the corrosion we see in that second photo :

Am I correct in supposing that all of the tubing and tank are aluminum ? How many years has the tank been in service ?

What this is leading to is that mysterious tube down at the bottom of the second picture :

What is this tube for ? Does it carry any fluid ?

I know, questions, questions, questions. Humour me.

 

[dkinzer]

Am I correct in supposing that all of the tubing and tank are aluminum ? How many years has the tank been in service ?

Yes, aluminum. I assume that this is the original water heater on a 2007 boat, so about 20 years.

Any idea what's causing the corrosion we see in that second photo

It is mineral deposit. I suspect that periodic flushing of the tank would be a good idea.

We've previously owned several different travel trailers and each of them had a magnesium anode in the water that needed to be replaced periodically - usually every year. Kuuma makes a combination anode/drain valve that screws into the drain fitting so that might help.

What this is leading to is that mysterious tube down at the bottom of the second picture :

That is the electric heating element. It screws into a fitting on the end of the tank and can be replaced if it burns out.

 

[dlochner]

I am in the process of re-configuring our Webasto diesel heater to that we can switch between having the engine heat the domestic water and having the Webasto heat it. The significance of that is that I was going to have to partially drain the antifreeze out of the water heater and the hoses between it and the engine so the timing of this failure was fortuitous.

Sure Marine sells a neat heat exchanger to heat the water tank if you are using a hydronic heater. The heating fluid goes through the heat exchanger and then into the HW tank. Engine coolant also goes into the heat exchanger and warms the heating fluid. This allows the HW tank and the rest of the heating system to heat the boat when the engine is running, saving diesel and wear and tear on the heater.

 

[dkinzer]

Sure Marine sells a neat heat exchanger to heat the water tank if you are using a hydronic heater.

Yes, I had seen that and considered using it but opted instead to use 3-way valves.

 

[Ralph Johnstone]

Kuuma makes a combination anode/drain valve that screws into the drain fitting so that might help.

Might be a good idea. Those spots look more like corrosion than deposition so I'd suggest throwing the anode /drain at it just for good luck.

 

[FastOlson]

Ouch. So sorry to hear about the hole! FWIW, aluminum tanks for fresh water systems have been a poor idea since Hunter started using aluminum for many/all of their internal tankage back in the 80's. While good for diesel they were very poor for waste and not so good for fresh water. Common material from many builders, tho, for water tanks. I threw away the OEM hot water tank in our '88 boat back in the 90's with its internal alum. tank and corroded outer painted steel shell. That material was sending little bits of white aluminum oxide thru the water system.
I replaced it with an SS tank - shell SS also. No problems since. Of course just mentioning this could invoke a curse from the gods of random corrosion!
Good luck on the replacement.

Edit: Similar to Dave's heating solution, I plumbed in a little heater/fan unit many years ago in our main cabin. It uses the hose carrying engine coolant first to the hot water tank to provide oodles of engine waste heat when under power. Brand is "Heatercraft" if anyone's interested. This concept is like the heater in a car (ICE).