Shower pump pipework help please

[Running Eagle]

My 10 year old 1.4 bar (twin) shower pump recently packed in and I bought a replacement PR50D 1.5 bar (twin) from B&Q. The old pump had 15mm push fit flexible connections. The new pump has 22mm push fit flexible connections. The pump is located at the base of the hot water tank. The cold tank is mounted high in the loft, say >3m head. There are numerous elbows and bends within 1.5 metres of the pump: 4 elbows plus 2 x 90 degree bends (worst case) and 3 elbows plus 1 x 90 degree bend (best case!). This is not my design! The shower is 10m away via 15mm copper pipe. I cannot replace the 15mm pipes to the shower.

Question 1: what are the problems with fitting 22mm to 15mm reducers at the pump?

On installation, I ran the shower without the pump working: cold OK, no hot. I ran the shower briefly with the pump working: cold OK, no hot. I put mains pressure through the hot feed to the shower: no flow. When I disconnected, less than half a pint drained out. I conclude the hot feed to the shower is blocked close to the pump (which probably caused the original pump to fail).

Question 2: is a hot water pipe blockage common?
Question 3: are the numerous elbows the root cause?
Question 4: if mains and 1.5 bar cannot shift a block in one direction, is there any point in trying in the reverse direction?

I could re-route the pipes at the pump and replace all but 1 elbow, but I will have to re-route the timer/programmer.

Question 5: will this be worthwhile?

Opinions and views welcome.

 

[flameport]

1. Cavitation, lack of flow, damage to the pump. Or perhaps none of those. Or maybe some of those.

2. No. Far more likely is the shower valve or inlet filter is blocked.

3. Probably not, but they certainly won't help matters.

4. Maybe, but check the shower first.

5. If you want this to work, then it needs to be installed properly.

 

[Running Eagle]

Many thanks.

Re 2: the shower mixer has been disassembled; no blockage there. The inlet filter is clear.
Re 5: it was orignally installed professionally, allegedly, although the numerous elbows suggest otherwise.

There is no way to change to 22mm throughout and the shower is 15mm anyway. I am stuck with a 22mm pump and 15mm pipes (and a blockage). I will disassemble the pipework above the elbows and see where we go from there.

Many thanks again.