I changed a pair of taps for a customer a few weeks ago, and ever since, they have complained about the lack of flow from the hot tap. I've gone through everything to check I have done nothing wrong, but found no fault at all. The flow from the basin tap is also pretty poor, but no overly so. The downstairs kitchen hot tap does flow better. All cold taps are connected direct to the mains, and run fine.
I'm coming to think that the main fault is lack of head from the HW cylinder, combined with a poor arrangement, where the HW pipe is 22mm from the cylinder for around 2 metres, then changes to 15mm pipe for the last 2 metres to the bathroom. The HW cylinder sits at floor level upstairs, with the feeder tank just above it, so not a lot of head above the sink level really.
I've suggested they get rid of the 15mm pipe, and run 22mm at least until the bath tap, and that should help. The nagging doubt in the back of my head is that when I do this, the flow rate will still not improve markedly, so I'll look an idiot doing the job, but getting no result.
Has anyone done such a thing? And did it improve matters? Thanks Alan.