Help....where's that bleed-valve (hot water cylinder)?

[confused of Bromsgrove]

Browsing existing topics, I'm sure I've got an air-lock somewhere in the hot-water cylinder circuit (traditional pumped/vented system, water only heats up with immersion-heater, gas-boiler works fine for CH, but cuts out after a couple of minutes with just HW on). Advice seems to be...
.... bleed the air out via the bleed-valve on the top of the two pipes going into the cylinder.....BUT I CAN'T SEE ANY MEANS OF BLEEDING IT!
Both of the heat exchanger pipes attach to the cylinder with just simple threaded unions...no evidence of any means of bleeding it. Would it be possible to just loosen the top union and let the air out, tightening it quickly as soon as water comes out? Or have I missed the point completely?

Any help & advice would be greatly appreciated.

 

[ChrisR]

Would it be possible to just loosen the top union and let the air out, tightening it quickly as soon as water comes out?

Quite so. Technically known as cracking yer nuts.

 

[confused of Bromsgrove]

Would it be possible to just loosen the top union and let the air out, tightening it quickly as soon as water comes out?

Quite so. Technically known as cracking yer nuts.

Thank you....I'll try cracking my nuts then. Just hope I don't wrench my pipe.