Go in the trailer and set the thermostat to 70 degrees. If the fan comes on within 20 seconds or so stand at the unit and count seconds to 20 within that 20 seconds you should hear a click. If you hear a click the main gas valve has opened and the heater should work. If this is the case I would not rely on the thermostat as a means of setting the temperature. They are not that accurate.
If you did not hear a click I have to ask. Have you had the gas bottles off since the heat last worked as expected? If so you may have air in the lines and the heater will not purge that air. At the heater crack the gas line till you smell gas and then tighten the gas line and try lighting the heater again.
If this works I doubt there was anything wrong with the board. Dealer like to change them because of the cost.
WBCCI 12156 AIR 3144 WACHUNG TAC NJ6
2004 Excursion 4x4
1991 34 ft. Excella +220,000 miles, new laminated flooring, new upholstery, new 3200 lbs axles