Lost Hot Water feed Upstairs

Changing the shower has produced this problem. The shower is a hot/cold feed power shower. The hot water is fed from a tank in the downstairs kitchen. This is heated from the Vokera ch boiler in the same room. The cold water feed is from the header tank in the loft. Today I shut off the water feeds to the shower pipes and after a small soaking from the water lying in the pipes seemed to have the situation under control. I was then able to measure up, for the shower unit to be connected to the electrics and to the tiled wall. In this meantime the kitchen lost it hot water supply! While the water supply to the shower was isolated I opened the only valves I had closed in order to restore the hot water supply to the hot water pipes. I now have hot water in the kitchen and no supply to the upstairs at all! Baffled I am suspecting an air lock but how do I overcome this? Anyone? Thanks in advance

Was any of the valves that u closed red head wheel gate valve,s cos they can jam shut & the spindle snap when u open them, there will be a stop & start position on these valves, if it just keeps spinning then its snapped. Then it needs changing & thats a great job with a tank full of water above it.

If an air lock, try a search - has been well covered.

bab - the wheel gate valves are for the cold water feed from the header tank and from the hot water feed from the pipe to the bath so I think I can rule those out. Thanks for the warnig about them snapping/sticking I'll be respectful of their age from now