Heating but no hot water

Having refilled the heating system and bled all the radiators succesfully, I do not have any hot water, which leads me to think that there must be an air lock in the coil circuit in the hot water tank. The boiler I have is a Worcester Danesmoor 15/19, with two connections in the top and two in the bottom. I believe one circuit is for the heating and one for the hot water. The only bleed I can find is on one of the bottom connections, but this seems to be on the radiator circuit.

Could there be an air lock in the coil circuit, and if so how do I get it out. Would I have to drain down the hole system again, and refill, if so how do I prevent another air lock.

Check for any 'thumb vents' near the cylinder. They are usually brass with a small screw cap on them -open them slowly until water or air is released - do not remove the caps completly as you will have water shooting out of them and its a given that you will drop the cap and end up standing in the cupboard with your finger over the vent for hours on end!

The only thumb vent near the cylinder is not on the circuit that goes through the coil of the tank. Any other suggestions would be most welcome.