Pump won't stay primed

[RoverAbraham]

Classic issue for diagnosis: pool pump won't stay primed - immediately after pump turns off (auto or manual) I can see air bubbling up from the pump suction line into the pump strainer. Is this a leak in the pump suction pipes?

I have the pump running on auto during the day with short gaps of an hour or so between runs so that it is able to maintain its water (even run it for a chunk during the night). Though I have to fill up the pump at the strainer every other day, so that isn't really a good/reliable solution. The pump won't run for too long if it isn't getting any flow, so can't cook it self - a positive at least.

Problem details:
Pump, sand filter and salt chlorinator unit (FilterMatster) all sit about 3 metres elevation above pool skimmer. Non-return valve (NRV) is fitted just beyond skimmer. Pool water level is fine in relation to the skimmer and skimmer weir gate operates fine (not jammed).

Pump was recently installed (in autumn) by pool peeps and seemed to run OK to part of the winter. The problem came along and now it's summer, so not ideal for trying to maintain the pool health.

Salt chlorinator (which is made of clear plastic so can be seen into) is after the sand filter - and sits higher than both pump and filter - has air bubble up into it at the same time as the pump strainer. Loses water completely out of the chlorinator.

The pool guys disconnected the pipework to the roof solar tubes recently, thinking this might solve the issue. But alas, no joy - the problem persists.

The suction line NRV just after the skimmer has a clear top on it. I've noticed the odd little twig or leaf in there and stop it sealing completely (debris must get through the skimmer basket). I can see this being an issue sometimes, and clean out the debris, but the problem seems to be there when there is no debris I can see propping open the NRV.

Where is the water going, and how is the air getting in?

[Teapot1]

I think you are right with the NVR, at 3 m head even the tiniest bit of dirt debris or gunk build up could give you issue. Time for a thorough clean. Then look at other bits if it doesn't stop.

[Denniswiseman]

I think you are right with the NVR, at 3 m head even the tiniest bit of dirt debris or gunk build up could give you issue. Time for a thorough clean. Then look at other bits if it doesn't stop.

Seconded
You could also check for air in the filter as that will compress and send water back through the faulty NRV
I had it and it blew the lid off the skimmer basket

[RoverAbraham]

I think you are right with the NVR, at 3 m head even the tiniest bit of dirt debris or gunk build up could give you issue. Time for a thorough clean. Then look at other bits if it doesn't stop.

Seconded
You could also check for air in the filter as that will compress and send water back through the faulty NRV
I had it and it blew the lid off the skimmer basket

Thanks. How do I check for air in the filter, and how would I purge the air put of it?

[Denniswiseman]

Some have air vents on the top or there is a pipe inside the filter which allows it to be vented into the returns