Warning Light Comes On..

[Davidkent]

Hey all.

Got a 56 1.8 TDCi focus here.

For some reason, after 140 ish miles the red cog ! Warning light comes on, more or less without fail and the car loses a touch Of power.

This distance is slowly becoming lesser and lesser distances and the car started a little lumpy this morning.

This light seems to point to glow plug problems, and when stopped for 5 mins, it'll start and drive fine with no lights.

Has anyone had this?

Seems very odd to me but can glow plugs or the relay do this?

Help much appreciated

Thanks

David