I think we have an air lock in hot bath tap?

But the plumbers who worked on our system have said its not an air lock but sediment from the cold supply tank thats blocked the tap. Could this be right? the tap is inaccessable at the back of the bath and i think the just dont want to fix it. They have tried re draining the system to no affect. The taps still spluttering and running low. No other taps in the house are afffected