i changed a tap washer in a down stairs cloakroom sink and after turning the hot water back on no water came from this tap. All the hot taps in the rest of the house are fine.The system is gravity fed.
Sounds like you have an old system which was installed a while back when air locks were not considered. Its a bit crude but i have cleared the same problem by linking the cold (assuming it mains) to the hot spout with a hose and blastsing/back filling for just a few seconds with mains water. This will often clear the air lock and makes light work of fixing the problem. You can do this on the heating system as well but its a bit more tricky and i wpouldnt recommend it
Hi - Sounds like you have an old system. If it happens again you could link the cold tap spout (assuming its mains) to the hot tap spout with a short hose and blast mains back up the hot which should clear the air lock. Hope that does the trick, only a few seconds blast no more!