Install hot water heater

[Hargus]

Hello,
       I'm about to install (replace) an Atwood hot water heater in my (new to me) 1990 Starcraft Starmaster. I went to my rv dealer and he was nice enough to test the old one and found a crack in the tank. He wanted $400.00 for a new hot water heater and to install. I found a new one online for $200.00. It seems cut and dry and not rocket science to install, since I'll just back the old out and replace with the new.
 My question is the test is (and use since this is my first pu with hot water). I was with my rv dealer when he tested the old. Needless to say he was testing the tank to see if it would hold pressure and not leak. I got confused when he filled not only the hot water tank, but the holding tank as well. Maybe to see if the hot water would work on both systems? We didn't get very far because the old had a small leak. So I never went the whole route with the hot water heater.
What is the best product to use as a seal on the outside of the pu when I push the unit against and into the pu.
 I'm not that familar with the holding tank and pump since I don't usually dry camp and have always used the water direct from the hook up to the sink on my other pu. I've only used this pu a couple of times since I got it (I bypassed the hot water heater and just used cold, I was used to it.) so I'm looking forward to have the use of hot water and understanding my plumbing system.
Thanks,
Hargus

[tlhdoc]

He may have been going to test the electric water pump when he filled the water heater.  To use the water heater you need to fill it and vent the extra air out of the hot water line, by opening your hot water faucet(s).  Then you need to light the water heater.  Use a long lighter to do this.  I am assuming that you have directions on where to light it.  You can use either a city water connection or the holding tank with the electric water pump with the hot water system.  Good luck with the instillation.

[SkipP]

Hello,
I'm about to install (replace) an Atwood hot water heater in my (new to me) 1990 Starcraft Starmaster. I went to my rv dealer and he was nice enough to test the old one and found a crack in the tank. He wanted $400.00 for a new hot water heater and to install. I found a new one online for $200.00. It seems cut and dry and not rocket science to install, since I'll just back the old out and replace with the new.
My question is the test is (and use since this is my first pu with hot water). I was with my rv dealer when he tested the old. Needless to say he was testing the tank to see if it would hold pressure and not leak. I got confused when he filled not only the hot water tank, but the holding tank as well. Maybe to see if the hot water would work on both systems? We didn't get very far because the old had a small leak. So I never went the whole route with the hot water heater.
What is the best product to use as a seal on the outside of the pu when I push the unit against and into the pu.
I'm not that familar with the holding tank and pump since I don't usually dry camp and have always used the water direct from the hook up to the sink on my other pu. I've only used this pu a couple of times since I got it (I bypassed the hot water heater and just used cold, I was used to it.) so I'm looking forward to have the use of hot water and understanding my plumbing system.
Thanks,
Hargus

Most water systems on pop-ups operate about the same way. The holding tank is just that, it holds fresh, cold water if you are camping without facilities. This tank is at atmospheric pressure.
 
The fresh water tank supplies the water heater with it's water via the pump that will fill the water heater and then, once full, out the faucet. It's a "demand" type system meaning that as pressure drops in the water heater, the pump will activate to keep a steady flow. A check valve in or near the pump will keep the water in the heater from back-flowing into the fresh water tank.
 
For the system to work properly, the water heater must be completely flooded, meaning you have to vent the air out of the heater.
 
Hope some of this helps!