Grohe wireless pumped shower

[GARYF123]

Hi,
Called to a job where the above was fitted (type 36022). Customer having to usually lower shower hose to get water flowing and temperature fluctuating (lack of hot).
Unit mounted in loft.
Cold feed from 15mm tank connector at side of unit.
Hot feed taken from horizontal take off on cylinder which is about 400mm below the Grohe unit in airing cupboard. It is tee'd off in 22mm Speedfit then immediately reduced to 15mm and routed through ceiling into Grohe unit with a series of 15mm Speedfit fittings!
Obviously, this is where I believe the problem lies!
Any suggestions as to improving the hot pipework? I was thinking of removing the Speedfit and fitting a copper 22mm tee from the horizontal take off but cannot decide whether to bring the pipe out towards the front of the cupboard a short distance then vertical in 22mm and elbow/reduce to 15mm next to Grohe.
Would it be a good idea to form a 'U' bend when coming off horizontal take off to reduce any air locks?
Many thanks in advance,

Gary.

 

[picasso]

Use a surrey flange off the top of the cylinder and fit a automatic air vent on the highest point of the hot pipework.

 

[Charnwood]

Are the water supplies within the unit's parameters; 0.1 to 1 bar?
What is the vertical distance from tank to showerhead?

 

[GARYF123]

Are the water supplies within the unit's parameters; 0.1 to 1 bar?
What is the vertical distance from tank to showerhead?

Thanks for reply.
Did not measure the water pressure as the mixer valve in main bathroom is fine.
The vertical distance from bottom of cold tank to shower head is approx' 450mm but is this relevant as the unit is pumped?

Gary.

 

[Charnwood]

450mm would give you 0.045 bar. Less than half the minimum recommended pressure.

It's pumped, so what. It's minimum requirement is not being achieved.
Page 6 and 8; Minimum pressure and Priming of pump may be needed if under 0.1 bar.
https://docs.google.com/viewer?url=http://www.plumbworld.co.uk/link/1/pwgh0062pumpedinstallation.pdf

 

[GARYF123]

450mm would give you 0.045 bar. Less than half the minimum recommended pressure.

It's pumped, so what. It's minimum requirement is not being achieved.
Page 6 and 8; Minimum pressure and Priming of pump may be needed if under 0.1 bar.
https://docs.google.com/viewer?url=http://www.plumbworld.co.uk/link/1/pwgh0062pumpedinstallation.pdf

Am I missing something?
The instruction, as I understand it anyway states that the recommended inlet pressure is 0.1bar. It then says if between 0.1bar & 0.01bar, priming may be needed. Does this not mean initially to get pump running without running dry? If that is the case then surely the fact that it is pumped does make a difference?

Gary.

 

[Charnwood]

Customer having to usually lower shower hose to get water flowing and temperature fluctuating (lack of hot).

The customer is having to prime it when they use it by the sounds of it.
The recommended minimum pressure, as stated in the MIs is 1.0 bar, 10 kpa, 1 metre head.

Rig up a 10 gallon tank at 1 metre plus above the showerhead, attach this to shower's hot and cold feeds, set shower to cold, run shower.

You never know.