Some common reasons why the Hydro Flame furnace in your RV isn't working include improper voltage levels, dirt inside the blower wheels, and malfunctions involving individual moving parts. If voltage levels at the furnace are too low, the blower will not have enough power to run and produce heat; if too high, the circuit breaker may trip. Debris stuck in blower wheels will cause it to run loudly. Lastly, because every moving part must work synchronously, one or more parts may fail and cause problems throughout.
Check the voltage if the blower does not work; a tripped circuit breaker is a common result of mismatched voltage. The furnace connection should supply at least 10.5 volts DC and not exceed 14.5 volts DC at the furnace; AC voltage should be between 105 volts and not exceed 135. Refer to your owner's manual for specific model limits prior to changing power sources.
Check for dirt in the blower wheel. While high voltage can cause the blower to run loudly, debris can get caught in the wheel as well. Disconnect the furnace from its power source, wait until the blower stops and then remove the debris.
Check the startup sequence to determine where the furnace malfunctions. First, the fan relay coil should energize between 15 and 20 seconds after the contacts on the thermostat close. Second, the motor should start to turn the combustion and air blower wheels. Then, in 1 to 2 seconds, the blower will reach the required revolutions per minute (RPM) to shut the air-operated sail switch. Finally, the temperature limit switch sends current to open the gas valve, after which the flame should ignite.