HW airlock problem

[long story shortened...]
House is 2 floors + attic. Pipes go from CW tank in attic, down ~~ 8 ft to HWC on floor 1, back up to attic, along ~~ 10 ft and down to bathroom also floor 1 . There they run horiz. for about 6 ft, then 2-3 ft up to taps. Recently I had to drain, turned supply back on, no water. So I cut the pipe at the high point between HWC and bathroom, inserted a tee and a vent pipe.
1. If I fix the tee roughly level with base of CW tank, then the airlock doesnt clear, so no hot water.
If I fix it about a foot higher, then the airlock does clear, but
2. if you run the taps fast, the pressure drops so much that air gets sucked in through the vent pipe. and
3. if the CW tank gets half empty, the water cannot climb up to the tee and so you only get half a bath.
4. On the way from CW tank to bath, it goes through 4 service valves. Would you expect a better flow if you removed some of these?
Please any advice? Mark
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Fix it as low as possible (just above the HWC is good) and stick a bleed valve on the high horizontal section.
Christian.
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In an earlier contribution to this discussion,

The biggest miracle is that it's *ever* worked!
The only way to get a reliable hot water supply to the bath is to re-route the pipe to run between the ground floor ceiling and first floor floorboards - rather than going up and over.
--
Cheers,
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