shower pump not working

[halfax]

i have fittted a shower pump ( on gravity system) if i open the shower a bristan thermostatic controlled no hot water comes out nor does the pump kick in.if i crack the nut at the back the shower control,pump kicks in and hot water comes out of the shower. as soon as i shut off shower tighten nut back up ,the shower will not restart with hot water.
any ideas .
thanks.

 

[seco services]

have you got enough head, between the shower head and cws tank in loft ?
how is the pipework been installed, route it has taken

 

[halfax]

first thanks for taking time to reply.
the hot water feed goes from cylinder cupboard up into loft then down into shower.
the hot water pipe does not go higher than the cold storage tank it is 22mm.

 

[seco services]

will the pump start if you lower the showerhead down ?

 

[halfax]

no ,but if i open the hot water tap it works.

 

[Fluffster]

When was the system installed?
You may have a blockage in the filter mesh just before the shower valve.
Pete

 

[halfax]

have took filter out and they are ok. when i crack the valve nut at the back of the shower works great. then i turn off ,tighten it up and it will not run hot at all and pump does not kick in.

 

[seco services]

sounds like you don't have enough head to give good gravity flow to kick pump in.
ok without valve but when valve connected it has to go through the filter and non return valve fitted in the shower valve.