Gas and Oil Home Heating Furnaces - Gas furnace blowing cold air!

I bought my house during the summer and checked both the a/c and heat. They are 2 separate units in the house but blow through the same vents if that makes sense(you have to make sure one if OFF before running the other or they will both run at the same time).

The heat worked great until 3 days ago. It went from blowing HOT air to warm air, now ice cold air. The pilot is lit and it is blowing strong...but only cold air! I don't understand what could have happened! Please help!

BTW it is a Inter therm and model mgh-0758 AD 15(this is what the front says anyways)

Is the main burner going, or just the pilot light going?

the burner lights up, but seems like only on a very small low flame and now neither will even stay lit!

Sounds like low gas pressure...

Are you Nat. gas or LP Gas?

nat. gas...i can smell gas and if i put a lighter in there it will light...it just doesn't stay lit very long...i have already changed the thermal cup. i have been at this all day and nothing seems to be working.

the one time i got it all to stay lit i had to let the furnace run for 30mins before plugging in the fan and i finally got warm air! but as soon as it kicked off the burner went out again.

Sounds like your gas valve is acting up.. May be time to call for service, messing with the gas valve is not a good thing to do.

OK, so now things are a bit diff. apparently they copper wire was put in wrong(my dad came and checked it) so now it comes on and lights...everything lights fine burner and all...but it still blows cold air...now it is coming on for 5 or 10 mins then shuts its self off...then kicks back in with in a min or 2 and just keeps repeating this

Do you have a meter? Check power across the gas valve to see if you are getting 24 volts.