overheating problem on a mk1 punto?

The warning light glows after the car has been running for about 10 minutes. The head gasket has been changed & pressure tested. I have fitted a new thermosat, temperture sender & checked the timing. The car doesn't seem to get that hot no matter how long it is run, it doesn't lose any water & it doesn't boil up. I think it may be an electrical problem. Has anybody got any ideals please