disco11 v8i pressure in cooling system

i own a 199 disco 11 4lt v8 running on LPG
nice motor drives well when it is working properly
the head gasket when on it and i got a land rover garage to sort it out
heads skimmed new water pump and thermostat and drove it home some 15 miles when out in it one night to asda to get some cash while i was getting the said cash one of the small cooling pipes from the vapor camber had burst got the RAC out to sort it out and they did and drove it home i was advised bye the RAC man to change some of the other small pipes that looked a bit iffy
did them the next day started it up and tested for leaks and found none when for a run out later that day and had a look under the bonnet and found that the top hose that goes from the radiator to the thermostat had increast in size
so i take it that the engine is pressuring the cooling system
dose any one know what could be causing this
thanks ian (disco v8i)

check rad is hot all over so is cooling effectively, check top hose is hot proving thermostat opening,chech heater gets hot proving circulation,ensure system full and air bled, could be poor head gasket job ,if very hot 1st time head could have moved again,cracked bolck behind liner

Thanks for your reply
i have driven it back to the garage this morning about 15 miles it runs alright and it does not get any hotter than it should but the cooling pipe is still swelling up with all the pressure building up they are having a look at they have said it could be the new thermostat not working properly they are going to flush it out again and put on a new rad cap and a new thermostat and see how that go's from there

gas analyser sniff test over expansion bottle-if it jumps from residual under bonnet reading -then you have exhaust gases entering cooling system