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Well, neighbours have all sorts of differing systems (gravity-fed, old-fashioned hot-water tanks, etc), so not a great help. One says he had to have a pump fitted as his gravity-fed shower wasn't doing the job, but with the electric pump it was okay.
Having had my shower today at 0800 (i.e. peak time for showering round here, I would guess), and having had to 'use' the bath-tap trick to activate the shower, I'm still mighty suspicious of the water-pressure.
Solution could be to get up very early and miss the rush, or wait till later, same reason.
When we measure the flow, it's right on 15 lpm through the other taps, and right on 10 lpm for the shower, so I imagine that if it drops a little, say down to 8 or 9 litres per minute, it just won't make the boiler kick in.
Anything non-drastic we could do? It's a very small London flat, so we haven't got room for big water tanks/hot-water storage/etc, so I don't see where we could put a pump into the system to increase the flow.
Is replacing the cartridge very tricky? That, along with the hose and head, are the only parts we can get at.
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