Megaflo: Trouble recharging the air gap

[jacks7]

I'm having a harder time than I think I should when attempting to recharge the air gap on my Megaflo cylinder.

To make sure I'm doing this right: and I realise to some this will sound like a really basic question, which of these two valves is the cold water inlet to the Megaflo?

I thought it was the one nearest me (the one on the right of the photo). When I turn that valve off, and open the hot tap, only a trickle of water comes off and then no more.

 

[picasso]

The one on the left is the supply to the megaflo.

 

[jacks7]

Great, thanks. One other question: should I expect water to stop discharging from the hot tap and through the tundish at the same time?

When I attempted today, the water stopped from the hot tap very quickly but continued to discharge through the tundish

Edit: I would also add that there is no gurgling sound at all while doing this

 

[muggles]

Hateful things. Just fit an external expansion vessel.

Are you sure you're opening the correct valve? It's the one on the cylinder you need, not the one on the pipework