Trojan Boat Forum

OK, I give up. I'm sure it's an easy explanation, but so far I've "cooked" one heating element and am sure I've just about broiled the one I just installed the other day. I have an 11 gallon Atwood EHM11 electric water heater, installed in 2008 to replace the original Dayton that came installed on the mighty BH back in 1977. For the past two seasons it's worked great until this year. I launched in early May, filled the water tank (20 gal) and, I assumed, the water heater (11 gal). Made sure all the air was out of both the cold and hot water pipes in both sinks (head and galley).

When I turned on the power to the water heater for the first time last week, I noticed no hot water. I ran a continuity check on the element and got no reading. Ordered a new one ($21 bucks, big deal) and proceeded to get ready to replace it. When I went to drain the water tank (there is a drain with a faucet handle on the lower left), no water came out. I then unplugged both HW and CW lines and some water came out - certainly not 10-11 gallons worth - maybe a couple of gallons. I then removed the old element and more water came out. The old element looked like one that had not been in the water. Really nasty looking.

I replaced the element, attached the water lines and hooked up the electrical. I turned on the water pump and expected half my 20 gallon tank to go into the water heater. It only ran for a few seconds, maybe filling the water heater with 1-2 gallons. I opened up the hot water taps in the head and galley sinks and got some air and "burping" but then full water flow. So, I thought, okey dokey, ready to go. Turned on the power and a few hours later checked the water. It ran warn for a few seconds and then back to cold.

I THINK I did not fill the water heater because there is a lot of air trapped in it. The water fill and water exit fillings are on the bottom of the unit and the p-t valve is near the top. Should I have opened the p-t valve when I turned on the water pump, and this would have allowed the air on top to bleed out? Like I said the unit is only a couple of years old and I am no HVAC/plumbing guy.

Any thoughts and other words of wisdom (before I go buy ANOTHER heating element to replace the one I most likely burned out)????

Thanks

the little thingy that tells the element to kick in is bad and not turning it on would be my guess. check and see if 110 is going from the 1st one then to the 2nd down to the element, also there should be a reset button on the top one. As far getting the air out can you hook up to city water more pressure could help.

Something aint right with your plumbing. No way a water heater is going to work with both the inlet and outlet on the bottom. The outlet has to be on the top to keep the air purged out.

Do you decomission the water system for the winter in your area, would you have removed the water lines at one point?

Do you have 2 or 4 water connections on the tank? My thought is that you've hooked the fresh water lines to the heat exchanger (if applicable) that should run off the engine. This would still give you water at the taps, you would still get a little air but would seem like the tank filled quicker than expected. The two exchanger lines are usually in the middle of the fresh water lines with cold coming in on the bottom and hot exiting close to the top of the tank.

If the elements are indeed burning out, they were most likely dry when turned on. They won't last very long dry but maybe long enough to heat water you had in the exchanger coil. Perhaps that's why you got a little hot water out the faucet.

Thanks for the replies. I just talked to Atwood and they said to open the relief valve to let the air escape. I've got the hoses hooked up right, and not to the heat exchanger, where they have never been hooked up, since the boat is raw water cooled. I may have cooked the replacement element, but that I can tackle again. The connections for cold water (in) and hot water (out) are on the bottom. The relief valve is on the top, so that explains why I am trapping air when I try to fill the water heater tank without relieving the air out of the top.

Duhhhhh. Now I go drag my knuckles back to the boat.....

Obviously a poor design. You don't have to bleed the air out of your house water heater after you drain it.

I'm having a problem with this one. Something just isn't making sense. Never ever had to do that before. I'm with DB. Either there's something else going on or it's a bad design. Curious to see if Attwood's suggestion resolves the issue long term.

Danny Bailey wrote:Obviously a poor design. You don't have to bleed the air out of your house water heater after you drain it.

Agree 100%

I may be wrong, but in my experience hot water tanks always feed cold water from the bottom, and draw off hot water from the top.
Is it possible a bypass was put in when the tank was winterized? That's how I winterize my hot water tank.

Being bypassed is certainly a possibility. It's hard not to assume that some things have already been checked! Curious though, if the vessel gets decommissioned off season, was Attwood's proceedure carried out in commissioning of '08 and '09? If it didn't need to be done before, why now?

When I look at the Atwood site documentation I see pipes (engine and water lines) that have one higher than the other [outlet A in diag 1]... so that outlet is in fact higher.
http://www.atwoodmobile.com/manuals/wat ... .19.07.pdf

They also say on startup to open nearest hot water faucet and run water pump until all air is gone..... Sounds like you did not do this long enough. ALSO...
Are you using after market heating elements?
They say this should not be done as they tend to run too hot and burn out early... the Atwood element has protection against run dry burnout.

NOTE.. the design uses an air gap at the top of the tank, see pg 2 "to replace the air gap follow these steps".

You may just be using the wrong heating element...

Thanks all. Just for the record: Both the cold water and hot water connections (in and out) are on the BOTTOM of the tank. There are connections for manifold if you want to run engine coolant through it (if you have a FW cooled marine engine or have an RV). I used Atwood heating element. With the in and out on the bottom of the tank it does make sense that you have to relieve the air on top of the water by opening the relief valve. Since the hot water taps in the boat are located just slightly above the outlet on the tank just opening the taps will not relieve the air pressure on top of the water level. Atwood does not say anything about this in any of the their literature, and it was only disclosed when I contacted them (and my engineer golf buddy told me the same thing). So far this is still the THEORY of the case until I get back on the boat tomorrow.

I'm confused... does your tank not look like the diagram on page 4 of the link I quoted above?
The outlet is above the inlet (just) but even more important way above the heater element.... I fail to understand how after running the hot tap you would still have air in the tank down to the element

Doe your tank fitting layout not look like the diagram on pg 4

The diagram is correct. My unit is the EHM 11. But the perspective of the diagram is misleading. The outlet is above the element and also above the inlet, but the pressure relief valve is much higher than what the diagram my seem to indicate. When I removed the outlet hose I got "some" water but most came out when I removed the inlet hose and element.

I get plenty of uninterrupted water flow from the hot water tap when the system is connected and the water pump is on, but that's because it's basically circulating water in and out just slightly above the outlet (or else I'd get a lot of air burping out of the tap). I also think my drain valve may be clogged, which I'll tend to tomorrow.

I seem to recall that when the tank was first installed in 2008 it had a lot of residual water that drained when I turned off the water system pump and opened the hot water tap to relieve pressure in the system before I left the boat for extended periods. We used the water heater a lot that year on our canal trip, and had plenty of hot water.

Now when I do the same thing there is very little water that drains and it takes less than 10 seconds for the water pump to "top off" the water heater tank. All this leads me to believe that there is trapped air above the level of the current water "table" in the tank. The fact that Atwood doesn't mention bleeding air out of the tank when first filling it, but then tells me to do so when I contact them, is still a mystery. I'll let you know what's up after tomorrow.

Randy, can you post a picture of the hookup as it is now. That would really help us visualize what you're describing.