I have a 10 gallon hot water tank, I noticed if I leave the heater on using the gas the red light comes on very quickly. What does that mean? Also it leaks down the outside of the rig once it gets hot. Hubby replaced the valve so that's new and he also turned it down as far as it would go but it still leaks. I've been using the electric button to heat the water but it leaks after a while anyway.

Any ideas short of getting a whole new water heater?

The red light you ask about is it in the gas switch? if so it is the indicating light to let you know when the gas bruner is lit.  Also water expands as it heats up, the funny looking brass valve on the back side of the water heater is the pressure relief valve and often drips or dribbles particularly if the water heater has lost its expansion head, which is no big deal. This air pocket will form in the tank by design - however, it will be reduced over time by the everyday use of your water heater. Try the following but becareful the hot water from the heater can burn a person, if you don't feel comfortable call an RV tech. 

To replenish the air pocket:

1.       Turn off the water heater. (let the water cool, see No. 4) 

2.       Turn off the cold water supply line.

3.       Open a HW faucet in the RV.

4.       Pull out the handle of the pressure relief (P&T) valve and allow water to flow from the valve until it stops.

5.       Release the handle on the P&T valve - it should snap closed.

Close the faucet in the RV and turn on the cold water supply.
As the tank fills, the air pocket should develop. Repeat this procedure as often as needed to reduce the frequency of the weeping P&T valve. If the weeping persists see a qualified RV tech, good luck hope this helps.
 
 
Flyone 
 

-- Edited by flyone on Thursday 5th of November 2009 12:58:42 PM

We also had some leakage  everytime our hot water heater would heat up. I did a little research and found out that they have anode rod inside them that need to be replaced.  These keep the water heater from corrosion.  When I took ours out it was completly gone.  So I replaced the anode rod ( approx $8.00).  When i did this I also flushed the water heater out with clean water which cleaned out a bunch of deposits.  I then filled it back up and did the above step to make sure that there was an air pocket.  I am happy to say that we have not had a problem since.  Hope this helps.  

John and Terri