No coolant flow

[audisport8680]

just realized I posted in wrong section so I will re post here. Things are progressing slowly with "84 coupe with 7a 20v that was in it when I bought it, I managed to get it running fine, It had no idle control valve in it, so fitted that and fixed some burnt breather pipes and a good service and runs really well now. My problem I have notice now is there is no coolant flow back into the header/expansion tank, after idling for half an hour all the pipes are hot, fan kicks in fine, cabin temps adjust fine but still no flow from the top of the rad via small pipe into the tank. coolant in the tank remains cold and when you take cap off no pressure at all. The only pipes that dont get hot are small one from top of rad into tank and small one at bottom of tank going to bottom of rad. I know this is not right, I can blow through the whole system and see bubbles in the tank so appears no blockage, has had new water pump and stat fitted. Any suggestions? thanks as always ***** APOLOGIES FOR THIS APPEARING TWICE****

[missfire]

No blockages and no pressure must be the pressure cap on the tank blown/stuck open?? Any signs of previous coolant explosions through the cap? Stains on bonnet soundproofing if it has any? Sorry don't know the 7a plumbing but does sound weird! The only other weird thing I've heard is plastic pump impellers snapped off but normally takes some amount of miles for that to happen.