I have a MGHA056AAFC02 MOBILE HOME FURNACE that is blowing cold air. The pilot is on and stays lit, when you turn the thermostat up to call for heat there is a click the blower starts but the burner never ignites. Ay help would be greatly appreciated.

SOURCE: Rheem gas furnace pilot lights, but no burners or fan

If the burners do not fully ignite, the sensor will shut the furnace down. The lack of sufficient burner flame is a gas valve or gas pressure problem within the valve.
Replacing the gas valve with the original one may get you going. I surely suggest a professional service company for safety reasons and a thorough inspection. A 20 year old furnace is past it's normal life span.

SOURCE: York Dianond 80 Furnace

You have a limit switch that needs to be reset. It is probably the roll out switch that is located on the burner housing. The limit switch is a disk about the size of a dime or penny and has two wires to it. There is a small button in the middle of these two wires. Press this button firmly to reset it. Look for all the limits that may be on the unit that is manual reset like the one described above and do the same. This should correct your problem.

SOURCE: having a problem with a goodman gas furnace, pilot

Sounds like the rollout is being tripped from the blower moving the falmes. i would have your heat exchanger checked for cracks or holes as this is usually the reason the blower moves the burner flames to tripp a rollout.

SOURCE: We have a coleman mach

Check to see if you have proper voltage and enough gas pressure. Look to see if the fan motor is turning; the fan motor could be bad. At times, the intake vents may be dirty and blocked. If this is the case, clean the vents and the blower should start working. The problem could also be caused from a bad sail or limit switch that can be replaced. Look at the electrode to see if it is at the proper adjustment and the wires are connected and not burned out. Finally, check the gas valve. The valve could be bad, have a dirty burner or a bad control board. your Suburban RV furnace's burner does not ignite or stay lit. This could be from the gas pressure being low. The exhaust and intake air vents could be closed or blocked. This fix is easy because you need to clean out the vents with a wire brush. The problem could also be as simple as a dirty burner. If something is wrong with the electrode or control board, the burner will not ignite. Again, check the voltage, and if it is not at the levels your owner's manual suggests, see a professional at your local RV dealer to fix it.

SOURCE: Janitrol GUPS075-3 Furnace burners will not stay lit

The first thing I would do is make sure the flame sensor is clean, this is a metal rod immersed in the burner flame on the opposite side of the igniter. If too much oxidation builds up on it, it will not allow the burner to stay lit. To clean, just turn off furnace and remove flame sensor and clean with steel wool and then reinstall. If this does not solve the problem there may be a problem with the gas valve.