Temp warning light came on so pulls over. Top of radiator boiling hot, bottom freezing cold. Loads of air in system, flushed it out and as the water coming out of valve was brown. Filled it back up with water, carried on and drove the 30 miles back home and all was fine. Also, the heaters werent working when I used my car last weekend but I didnt think much of it. After the minor scare today and I flushed the air out the heaters now work. Had the head gasket replaced completely last year, around September 2005. Reckon its gone again? Only had it serviced and MOT'd back in July. What can cause air entering the system?

Its a 1.1 mk 1 Punto S

If the water is brown and sludgy then your head gasket has gone and water is getting in the coolant system. blown head gaskets can also casue over heating.

Gutted. Luckily I have AA parts and labour cover. They will stop letting me have that soon!

Doesn't sound like the Head gasket to me. It sounds like there is a blockage ing the cooling system.

Could maybe be the thermostat..

If it was the head gasket, wouldnt the problem occur pretty much straight away? Last time head gasket went it was undriveable. This time I got I drove it 30 miles no problem straight after and I drove it for about 15 mins other day no problem and the heaters are still working. How long would I need to drive for it to occur again/

If it is the head gasket no point in me taking it garage off my own back because for the parts and labour cover to pay for it I need to call out breakdown service. If it does it again Ill just ring them and say temp light came on and lost power and they can diagnose it.

So how can air get into system in the first place?

i would drain n flush system, fit a new thermostat re fill with coolent and see if it still happens.
dont keep driving it because if the hg isnt gone it soon will be