I have noticed recently one of the return line jets to the pool is releasing a lot of bubbles, almost continuously. I put my hand over the other return jet, no bubble, but no water coming out of it either. Strange. I suspect a suction side leak somewhere that is pulling air in.
So I started to turn off the suction side valve one by one to test. My set up is I have 4 lines on the suction side, SPA, SKIMMER, CLEANER and MAIN DRAIN. Then they merge into one line into the inlet of the pump, then out of the pump to the filter, out the filter to another 3 way valve, one returns to the pool one to the spa, as pictured below.

I switched all the valves off then turned on skimmer only, cleaner only, main drain only, one at a time, and no difference, the bubbles continue to come out of one of the two return jets, with the other having no pressure at all.
My next step was to trouble shoot other places I may have a leak. Could be the pump strainer basket lid gasket, could be the threaded connection on the inlet side of the pump...so I wrapped some duct tape around everything just to see if I can at least get the pump to prime and rid of the bubbles. You can see in the picture below I have taped the lid and inlet connection just to see if it makes any difference. It didn't. I am going to try some shaving cream next around nearby joints next.

Then something dawned on me.
A few weeks ago, I was emptying the water from the spa intending to refill it from water from the pool. I do that by turning all suction lines from the pool off, and turn the spa suction line on. My intention is once the spa is full, I turned the suction line back to main drain from pool, and set the valve on the return line to the spa to refill it.
Well that didn't happen. I got distracted by a phone call, and after I hung up I went to do other things completely forgotten about this, until six hours later...the pump was running dry for hours as the spa doesn't take even 20 minutes to empty. I felt the pump at the time it was HOT. The piping connecting to it also quite hot. I turned it off and let it cool overnight before I turned it on again. It seems to run but had trouble priming. I think the bubbles from the return jet started at that time but I am not 100% positive.
Could the pump running dry for close to 6 hours damaged the pump or the piping connecting to it to have caused air to leak into the system?
So I started to turn off the suction side valve one by one to test. My set up is I have 4 lines on the suction side, SPA, SKIMMER, CLEANER and MAIN DRAIN. Then they merge into one line into the inlet of the pump, then out of the pump to the filter, out the filter to another 3 way valve, one returns to the pool one to the spa, as pictured below.

I switched all the valves off then turned on skimmer only, cleaner only, main drain only, one at a time, and no difference, the bubbles continue to come out of one of the two return jets, with the other having no pressure at all.
My next step was to trouble shoot other places I may have a leak. Could be the pump strainer basket lid gasket, could be the threaded connection on the inlet side of the pump...so I wrapped some duct tape around everything just to see if I can at least get the pump to prime and rid of the bubbles. You can see in the picture below I have taped the lid and inlet connection just to see if it makes any difference. It didn't. I am going to try some shaving cream next around nearby joints next.

Then something dawned on me.
A few weeks ago, I was emptying the water from the spa intending to refill it from water from the pool. I do that by turning all suction lines from the pool off, and turn the spa suction line on. My intention is once the spa is full, I turned the suction line back to main drain from pool, and set the valve on the return line to the spa to refill it.
Well that didn't happen. I got distracted by a phone call, and after I hung up I went to do other things completely forgotten about this, until six hours later...the pump was running dry for hours as the spa doesn't take even 20 minutes to empty. I felt the pump at the time it was HOT. The piping connecting to it also quite hot. I turned it off and let it cool overnight before I turned it on again. It seems to run but had trouble priming. I think the bubbles from the return jet started at that time but I am not 100% positive.
Could the pump running dry for close to 6 hours damaged the pump or the piping connecting to it to have caused air to leak into the system?