Remove the radiator hose, let all the water drain out.
Refill the system using just water for now, no point wasting anti-freeze. After re-filling to the min mark, start the engine leaving the radiator/filler tank cap off, leave it for 20mins running at idle, so any air can work out and it can get upto temperature. Squeeze the radiator and water hoses gently to ease bleeding of air around the system, but be carefull as the engine can get hot.
Is it any better after a drive? If so, give it a day and see what its like. REMEMBER TO ADD ANTI-FREEZE Again as you risk damage to water pump, head and cylinder block otherwise.
My mondeo which is similar engine to the Galaxy blew cold air out of the heater, it turned out to be the thermostat.
This is a cheap item to replace, around £13.00 from Ford. Its quite easy to fit, but ford will charge you £40.00+vat for fitting.
If that doesnt help, i would be looking at the water pump not working. If the water isnt going around the system, the heater will not get warm.....the temp will stay constant as theres enough air getting over it and short runs, but on a long run or hot day, it will overheat.
Hope this helps.
PS. Water pumps are about £50 for a pattern part, fitting will require timing belt removal and a new timing belt, so your talking £100-200, +vat +parts at a local garage. Lets hope its not that bad.
J P Evans, February 2006