No water at all at hw taps after draining vented cylinder

[olejim]

There was a leak at the feed pipe coming from the cold water tank. So i stopped the feed to the tank and drained the hw cylinder and tank by opening a tap, until both the cylinder and cold water tank were empty.

Fixed the leak, turned on the feed to the cold water tank, tank is full, the cylinder is full.
Turned on the heating, the pipes going to the heat exchanger (flow and return) are both very hot, not a boiler problem then. The vent pipe is very hot until 1 feet above the outlet and to the point where it dissapears through a wall. Turning on the immersion heater doesnt help either to create enough pressure to push the water through, when it reaches 60 degrees it just turns itself off.
There is cold water coming through the cold water taps, good pressure.
But when opening the hot water taps anywhere in the house, theres a bit of dribbling (warm-ish water) then stops, not water at all coming through.

There isnt a motorised valve on the dhw circuit, i looked.
I think there might be an air lock somewhere.
How do I get the water flowing through the how water taps?

I am VERY desperate, please help...need to take a shower.

 

[Burnerman]

I'm sure there will be some assistance in the FAQ's somewhere, but yes, you have an airlock.
Sometimes these can be very awkward to shift but essentially its a case of introducing mains pressure cold water into the hot tap of the affected sink.....this forces the trapped air up into the header tank.
The problem is how to do this......well, I've used a washing machine hose before, together with some Hozelock adaptors; if a mixer tap is involved then putting your palm tightly against the spout (hot tap open) then opening the cold sometimes works; I've even used a wet vacuum cleaner with yards of duct tape wrapped around the hose to pull the hot through.
John

 

[Space cat]

Yes, it's an airlock. It's a very common problem caused by bad pipe layout. (Somewhere along the cold feed pipe you have a slight upward slope.) All it takes is for the pipe to rise by its own diameter (22mm) and you trap a column of air in the vertical section below.

As Burnerman says, you can usually shift it by forcing mains pressure water into a hot tap. The mixer tap trick won't (or shouldn't) work with a kitchen mixer because it's not supposed to be a mixer at all. The two supplies emerge from separate holes in the spout.

PS: You can't drain a hot cylinder by opening taps. You need a drain cock at the bottom for that, which is something to think about if you ever fit a new one.

 

[olejim]

Thank you so much. It works! Easiest thing to try was the kitchen mixer spout (luckily it is a mixer), left the cold run through for like 30 seconds, and got my hot water back everywhere.
Phewww...