pump losing prime

[aussieta]

Hi. i have a secondary pump that is dedicated solar heating
it pumps to black hoses on roof of garage about ten foot head height
anyway it loses its prime after about 12 hours of being turned off
this means i can't leave it on automatic as there is no protection to turn off pump if no flow
there are no water leaks when operating and after primed and running for half an hour there are no bubbles in the return line
anybody have any tips to try and find where it is drawing in air when turned off.
thanks,
Andrew

 

[jblizzle]

Why is it bad for the solar to drain? Most panels are designed to do this by installing a vacuum release valve. If it reprimes when the pump turns back on, I am falling to see the problem.

 

[aussieta]

pump doesnt reprime, just cavitates
the system does not have a drain back, it is always meant to be full of water
anyway i think i may have found the problem one ot the union fittings up on the roof was damp
so i am hoping this was drawing in air when pump is off