i expect you will find after a drive they header will always have plenty of pressure
mien alws did generally cos tehy turbo is superheating teh water that goes thru it so its always over boiling point, no worrys when iys moving but when you stop it bubbles and pressures up

does teh fan work?
if it doeent you can bridge the sender (blue plug on side of stat housing where top rad hose goes) if its bridges and fan dont come on then its fook if its got power goin to it

has it got a big cooler? csn caus heat up when no air is flowing ie in traffic but a good slim fan will fix that
i had a grs on my estate and could do 140mph then less than a mile of slow to my house and would have thr turbo glowing under the car (burning grass too) but the fan always bought it back to where it should be with no hassle

fuel pumps can be had for a score 2nd hand new i think are about a 1'er and tuners can supply, msport delevlopments maybe

the heater matrix coudl be fucker and been bypassed, look on the bulkhead and if you see the pipes fucked with then you have to replace it