Jack
Two and a half years ago I bought my coach it has an Aquahot unit installed that had been bypassed so I set out to get it working
First after repairing fuel leak issues and getting the burner to work .
It became apparent very quickly it had problems the first thing was the tank bottom had a series of pin holes eaten through so it would constantly leak antifreeze when filled .
The second problem was I think related to the first , I think the system had been run low on antifreeze and had cracked the burner chamber causing it to leak antifreeze into the chamber when the burner was running and creating a large cloud of white smoke at the tail pipe.
After contacting Aqua hot and discovering that a new units price was outrages and a new tank was $9500 I decided I could do a lot of welding for that price.
The third problem was the domestic hot water coil had been frozen and was destroyed.
What I ended up doing is removing the unit and completely rebuilding it as follows
1) I removed the domestic hot water coil from the outside of the tank.
2) cut the bad section out of the bottom of the tank.
3) cut the burner combustion chamber out of the tank end plate.
4) located a wabosto 2010 coolant heater and cut the outer shell off the heat exchanger to ready the combustion chamber for installation. ( It was interesting to see that this is exactly what Aqua hot had done to build it in the first place.
5) welded the combustion chamber back into the tank end plate.
6) fabricate and replace tank bottom.
7) rap the tank with 160 feet of 1/2 copper tubing .
(the tubing came in 100 foot rolls so used it all 200 feet and as a result have better hot water production.)
incase the copper tubing in heat transfer cement
9) reassemble the unit into it's enclosure
10) reinstall into the coach
The completed unit looks and works just like a new one
I made all my welds with a mig welder and the welds have to be water tight
The system has worked flawlessly now for two years.
Hope this helps
Eric
Jack
With your unit for a temp fix you might drain and dry out the tank and try to pour an epoxy into the tank to seal the bottom .
Or if you can get to the bottom of the tank ( I don't think you can in the unclosed ) you might be able to use a screws and rubber washer to seal the hole the real problem is the tank is rusting out and the rest of the bottom is probably not far behind.
You could try stop leak but I'd try water glass instead you should be able to get it from a good old time pharmacy.
Good luck
Eric