We have a 2004 Beaver Marquis. It has the Aquahot model AHE-100-02S. The 02S model does not have a "control panel," per se, with status lights. Its controlling hardware is located on the upper inside of the Aquahot facing the square stainless steel box access door. There are no other buttons for the unit, other than its ON-OFF switch located in the living quarters. The ON-OFF switch's light should stay on when the Aquahot is alive and well. If the switch's light goes out, then the controlling hardware has detected a problem and will not allow starting the diesel burner, although the electric element should remain functioning... unless it's bad too. The electric element in our Aquahot provides enough hot water for two medium length showers.
How long since its last service? There are several items that can be your problem - in need of an annual service, flame sensor blocked, dirty filter, fouled diesel spray nozzle, bad igniter module, coolant too low, etc. An annual service will cost $200 to $300, not counting modules, if bad.