Pressure Build Up on Hoses and Overheating 2.5na 110. Help

Hi, just asking for advice, possible causes.

I've been noticing a pressure build-up on water hoses. In the winter I noticed the heater blower wasn't working, so that came out and it was the blower was sitting in water. All cleaned out and greased and all started to work again. When back together it wasn't blowing very warm at all so might be that the baffles around the heat matrix (was flushed through) were disintegrated and weren't replaced.

After a while I took it for a few short test drives and I noted that the hoses were pressuring and it was overheating a bit, so as a precaution I removed the thermostat just incase it was sticking. There was also a noticeable coolant loss (out of the header tank relief hose).

I've taken it out a few more times and yesterday noticed after 20 mile drive that as I arrived home, the header tank ****ed out steam and water for a few minutes, I'm guessing the cooling systems entire contents.

Of course I shouldn't have used the truck but needed to move something so nursed the old girl.

Wondering where to start. I'm based in Sweden with no local garages that I trust (used for another car unsuccessfully).

Any ideas what I might be dealing with?

Head gasket?

Yeah was thinking as much. No water in the oil. No strange exhaust emissions. My last head gasket was on a 205.

No odd engine performance. Just pressure building in header tank.

Could this be a seized water pump?