Have a 1997 Megane Scenic, heater only blowing cold air, no good in this cold weather!
Coolant level normal, temp gauge normal, and of the two pipes going into the heater matrix, one is lukewarm , the other is cold. This is where it gets more interesting - the radiator at normal temperature is cold from top to bottom. The water pump was changed in 2005, and Feb this year new temp sender and thermostat fitted. Help!!

Your heater core might be bad. If it is only blowing cold air out it means that your heater core has gone bad. They are not very costly.

Hope that helps. :]

hi best way is to try & clean out remove both pipes going to heater matrix going through bulk head & put a hose pipe in one & blast out any rubbish do this both ways a few times l would also recommend flush rest of cooling system on engine remove some pipes & flush hose in them as well do it both ways as this helps loosen any muck again do it a few times until water coming out is nice & clear.
just remember to put anti freeze in 50 / 50 mix that system holds about 5.5 to 6 litres. replace pipes fill up system bottle to max as u go squash pipes hoses to help air out, run engine & squash & re top up level fit cap & drive car to get really hot 5 miles or so u should be able to remove cap very slowly if themrostat open & adjust level to max try & make sure fan kicks in this sure happen when engine running with engine at fast idle 2,500 3,000 rpm this is easy way l find for people who r not mechanics there other ways but this is easy to explain. IT IS VERY UNLIKEY YOU WILL NEED A NEW HEATER MATRIX TRY THIS FIRST CHEAPEST WAY