Heater problem
2003 Vauxhall Vectra Two Wheel Drive Manual 103000 miles

hi,when stood still my temp gage goes up and i get warm airbut as soon as i start driving my temp gage goes down to zero and i have no heat.
i have flushed the rad system and then topped it up again.all the pipes are hot so water is getting through ok but problem is still there !!!

can you help please

thank you