Not that long ago the shower in my house was very good. It was an
Aqualisa thermostatic controlled mixer shower, probably 20 years old
but it provided a very good shower. The the problems started and the
pressure fell away so that the shower was poor. I thought it was the
showerhead so I de-scaled it, but with no improvement. I then changed
the head and hose, still with no improvement. Then I took the control
valve apart, cleaned it and having found no obvious problems put it
back together again. However, this shower which had previously been a
good hard flow remained a sluggish drizzle.

Thinking that the valve was shot, I replaced it with a new thermostatic
valve (Triton Izar). Still no improvement. Sincle then I have done the
following:

Replaced hose with large bore hose .
Replaced inlet connecters with 22mmto 3/4in bsp (was 22mm to 1/2in
bsp),
replaced isolation valves with new full bore lever valves.
Drained and flushed all pipes.

The shower is fed from a gravity cold tank about 1.8 meters above the
shower head and an oversized hot water tank, both through dedicated
22mm pipes. When I flushed the pipes the pressure was enough to
produce jets the length of the bath, so flow and pressure seems ok to
me.

I am now at a loss to see what is causing the low pressure in the
shower. It used to be ok, but now is not. Is this a problem with the
Triton shower, or should I raise the header tank ?