Does water (hot or cold) run when you open a faucet? It wasn't clear to me if you were having a problem only with the hot water (water pump is working but water not getting hot) or there was no water running at all. If there is no water running it would be an issue with the water pump. Either the switch to activate the pump is not on or the pump isn't getting power or the pump has failed. If you have water in your fresh water tank when you turn the pump switch on you should hear the pump operating. It will operate until a certain pressure has been achieved in the water line and then shut off.