Water Heater, Go out on me?

93 Coachmen Travel trailer, My brother has been staying it in for the past few weeks everything has been working good.. Last night he called me and said the water heater was'nt getting Hot anymore, so he swapped to a new propane bottle. Now the propane wont even lite, is the gas controlled by the valve at the water heater? Possibly some electronic went out and not allowing gas to flow through?