Audi Q5 2.0tdi possible head gasket

[Douglashowes]

Hi, I have a 2.0tdi year 2010 on 135,000 miles. 

Was recently loosing lots of Coolant and it turned out to the EGR cooler. Had this replaced but was still loosing Coolant. Put some steal seal in (https://www.steelseal.co.uk/) that seals headgaskets and other broken parts and it’s stopped the leak. However my Coolant system is very pressurised, the pipes are rock hard and there was air bubbles returning to the reservoir through both the return lines. There is no coolant loss just a very pressurised system. Had a block test done twice and there are no emissions within the Coolant system. Anyone had a similar issue? Garage is now saying it’s the head gasket but with no emissions in the coolant? Oil is fine and without leaks.