300 tdi cooling issue

Hi all
Firstly thanks in advance for any replys
I’m new to the 4x4 scene but a fairly competent mechanic however I’ve ran into a problem with my newly acquired disco 1
A week ago I noticed my heater stopped working followed by about 10 miles later my temp gauge creeping up. On inspection my coolant bottle has split on the join , no problem I ordered another and fitted , now the other issues began , firstly while refilling the system I noticed the system was pressurising pretty quick , to the point of coolant blowing around the bottle cap and the top hose getting firm , I then took the small bleed pipe off and found the y piece blocked , so this I unblocked and guessed that was the problem but on refitting I can’t get the heater to work and I seem to have a constant stream of air bubbles going back to the coolant bottle through the bleed pipe ! I’m guessing this isn’t normal ? It sits in the middle of the temp gauge and doesn’t over heat at all but still no heater ? My gut tells me head gasket failure but also no water in oil and clean exhaust gases ?
Many thanks

Have you filled it using the thermostat housing and the radiator fittng?

Cheers

Cheers

Hi yea I filled it through the rad then the thermostat housing but there seems to be a constant stream of air bubbles even after running it for around 30 mins
Cheers

Head gasket was my first thought and they can go in many ways I would say your compression gases are getting into the cooling system this would not give you oil in water or steam from the exhaust can be confirmed by a sniffer test.had it on a golf heaters stopped working then a hose burst replaced the hose 20 miles latter the heater matrix bursted no steam from the exhaust or any real coolant loss one further clue when the engine cooled off and released the coolant filler cap would give a loud pop or hiss.

That’s my suspicion Mr Glee , I’ve got a sniffer test coming so that’ll end any speculation, to be honest I’m pretty sure it’s the gasket which looks a fairly straight forward job so no real worries there , just finding the time to do it is more of an issue!!