UK Car Repair: vauxhall cdx 1.4 16v - overheating, radiator hoses, circulation problem

Question
Hi
My son has a Corsa to learn to drive in.  His temperature gauge goes to 100 within 5 minutes of starting (whether sitting in traffic or driving along) then the fan kicks in and takes it back down again, then we start all over again - every 5 minutes or so.  He has cold air blowing through even when switched to hot.  On the odd occasion when doing 50mph for about 5 minutes it does eventually start to blow warm, but immediately we slow down it goes cold again.  Is there anything he can check or do to solve the problem.  Any help would be appreciated

thanks
Eve

Answer
It sounds like an air lock in the cooling system, or perhaps even a water circulation problem.  Try re filling the system and bleeding out the air by squeezing the largest radiator hoses.  Is it actually getting hot, or is it a gauge/transmitter problem?