RV Repair: rv hot water heater, hot water heater, water switch

Question
I have a suburban h/w heater on a 89 cls a motorhome..if i start the rv and hit the hot water switch the light is bright red and the heater fires right up (gas) when i park and hook-up to 30amp service the heater will not fire up and the light is very dim..so i cut off the power,start the heater and reconnect every time i want hot water?

Answer
These units are usually hooked up for 12 volt operation only and work off of your batteries. I assume you have two batteries, one in the rear for the living space and one in the engine compartment. When the MH is running the heater will run off the alternator or aux power from the MH, when sitting without the motor running it runs off the rear battery and when plugged into shore power it runs off the rear battery. This meeans you may have a problem at the rear battery or charger/convertor. Check the rear battery first and the charger/convertor system. If this is ok then you are most likely going to have a short in the system. The heater will only have one power input so that would eliminate the WH as the problem.