Shower pump problem salamander ct60bu

[Rived36]

Evening all,
Finished a full bathroom 2 days ago
The system required a negative head pump to be installed (salamander ct60bu) as there was not enough head of pressure for a standard pump,
Here is the installation spec/layout,
The pump is installed at the base of the cylinder (1m below draw off) and connected via a surrey flange,
There is roughly 1.8 to 2m from the surrey flange to the tank connector in the loft,
And 1.5 meter head of pressure from the shower head to the base of the feed and expansion rank,
There are 2 air vents installed in the loft directly above the pump on the hot and cold feedto the shower,

Heres the problem,
The pump works perfectly fine and will run until the cows come home but,,,,,
Turn the shower off and leave for 10/15 minutes and the pump is air locked but only on the hot side,
The cold works perfectly fine,
All the technical parameters have been met and exceeded!
Any ideas before i request a warrenty call from salamander ?
Ive fitted hundredsof pumps in the last 20 years and never had this problem ???

ps, it as already been determined that air is not being sucked in via the vent,
Again once running it works fine until turned off,
Thanks in advance !

 

[rpm]

Can`t see it being a faulty pump, must be something to do with pipework. Faulty vent?

 

[SalamanderPumps]

Morning,

Just one quick suggestion - it might be worth turning the pump around, it will be a bit messy until you turn it back again but if you say the problem is on the hot side, have the hot swapped to cold and vice versa - if the problem remains on the hot side, we are looking at the system/shower and if the issue moves to the cold side, we are potentially looking at the pump. If it does appear to be the pump, feel free to give us a call on 01915162002 to speak to tech for further investigation.

Cheers