My MG 04 is under powered after changing head gasket?

My 04 MG 1.8litre, 29000 miles on the clock blew the head gasket. I got it repaired with the modified head gasket and the head was checked to see if it was crack but all is well. The car is driving perfect again but it doesn't seem to have the same power as it use to. The heater doesn't work on settings 1 or 2 but 3 and 4 are very powerful but no hot air comes out. The other thing is that when you put your foot to the floor on the accelerator pedal it only opens the trotle on the engine 3/4 could this be the engine power problem or is that the norm with the 1.8l engine.