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Another water heater replacement thread
Guess it is my turn. Can’t complain too much – they lasted 22 years. Marathon uses two 11 gal stacked heaters. The lower Atwood EHM11-SM is leaking. I can’t find a direct replacement but a Whale Seaward S1100 should fit.
I thought is was my P&T valve leaking draining through the supplied overflow. It did, but I missed that the heater core leaked too once warmed up. I did not catch it in time, so I get to replace the plywood they sit on. The laminate over the plywood hid the damage.
My question is: What is under the plywood? From below (road-side) I only see a foam layer. Is there a metal pan under the plywood? Or does the plywood sit in a metal frame with the foam directly applied to the plywood?
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8 Replies
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Marine grade plywood is attached to metal frame. Butyl tape between the metal frame and the ply. I coated the ply in epoxy, both sides and in the pre-drilled counter bored holes for the self taping screens. Pre-drill any openings for pipes and coat the inside of the holes all to prevent any water from wicking into the new floor.
You will likely find most of the ply damaged, expect to replace the entire bay floor. Most of mine came up without damage to the foam below. Still in place several years later. Use card board to make forms and builder supply foam to replace any that does come out.
I also replaced the rubber piping connectors, dump valves and put a modern camco sewer connection on the end. Since everything has to come out of the bay now is the time to refresh everything.
Big job but worth it.
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Thanks Joe! Helpful to know what I’m getting into. I still hope only the passenger side floor under the water heaters and pumps will need to be replaced. We shall see. Encapsulating the replacement in epoxy seems the way to go.
Home Depot has pressure treated 3/4 inch marine ply available. Shown as compatible with aluminum and iron fasteners. Might be another option.
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I am in the process of replacing my water heater. In another thread here on PC it was recommended to look at Raritan water heaters.
Ron
Jeff and Lindsay
91 Marathon XL -
About three years ago our bottom water heater also started leaking. Luckily we caught it before there was any floor damage. After a lot of research (and measuring) we discovered that direct replacement with two new 10 gallon Attwood models wouldn’t work…the current models are about 1″ taller and the shower drain was in the way. Fortunately we found a 20 gallon round heater that fit perfectly…at Lowes!
Jeff and Lindsay
91 Marathon XL -
to the person asking about what goes under the plywood flooring in the water bay, Marathon now uses a product called “King Starboard” for the flooring in the water bays. It is a synthetic product that will not rot. Marathon just re-did my water bay and that is what they used.
2000 Featherlite H3-45
2024 Jeep Grand Cherokee
Leesburg, FL -
Today I drained the water heaters and bypassed the leaking lower unit. I was able to reconfigure the existing fittings, check valves, hoses and pipes.
This brings up another question. There is a check valve in the cold water supply line to the heater and there is an expansion tank in the cold water line mostly to prevent the pumps from cycling unnecessarily.
There is no provision to deal with the hot water expansion itself which can be quite substantial. Online I found 4psi for every 1 deg F increase. Hot coolant at 200 deg F going through the heat exchanger would raise the pressure by 400 psi. Of course, the T&P valve would open around 150 psi. This would explain why the T&P valve always drips during heating.
If I did the math correctly, the expansion of an 11 gal water heater from 100 to 200 deg F would be about a quart. I’m pretty sure the few hoses in the hot water system would not be able to expand by a quart. Should there be an additional expansion tank on the hot water side? Does our system rely on the P&T valve leaking while heating?
But looking at my water heater at home, the expansion tank is also on the cold water side. No leaks from the P&T either. What am I missing?
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Our use of the water heater is unique compared to a normal plumbing situation. We turn the water heater off after every trip. When we turn it on the expansion takes place. I split the cold water filter housing once when the check valve failed open.
I reconfigured my piping such that the expansion tank is still on the cold water inlet but between the check valve and the water heater. No more worries about the expansion and the pump is variable speed slowing as it reaches the pressure set point so it really doesn’t care.
Jeff and Lindsay
91 Marathon XL -
Gerald,
I think you are correct to add a hot water expansion tank on the hot side of the check valve. A regular well accumulator tank technically should not be exposed to the temps it could see from the water heater. Make sure you get a hot water rated tank that is for potable water.
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