For the cooling system bleed,follow Oilyrags procedure in the previous posts.He knows what he's doing(well sort of!).I know him,we share the same mum and dad!
As for your fault,I would seriously get the
pressure checked at a garage with a proper test gauge,just to rule out any expensive problems!.If
pressure is suspect,then it will show itself when the engine is warm(
thinner) and on tick over(pump running slowly).
If the pressure checks out OK,then suspect the pressure switch(electrical switch that is activated by
pressure and when no pressure is detected it puts the dash light on).
It's strange for the temp and
lights to come on together.It could be a dash wiring/circuit board fault,but something must be triggering it.
I'd start with the
pressure,and go from there.(We are always here to help if you need it!)
By the way,where are you from exactly?