Hot Tub losing prime after 30-40 minutes?

[spishex]

Yeah, but you could take your pool/spa suction valve and close off all suction to the pump and get the same problem. That doesn't mean it has to do with what causes it during normal operation. It might be related, but digging out a new suction line isn't a very convenient solution.

Here's how I see it:
- In spa mode, your pump starts to lose prime in about 30 minutes.
- In pool mode, your pump works fine.

This narrows it down to one of two issues:
- There is a suction leak in the spa plumbing.
- There is too much head for the pump to handle in spa mode.

A big thing that we've all somehow overlooked is your filter. If it's dirty you could have enough suction to run it from the pool but not quite enough from the spa. That could also lead to low flow / gurgling from the heater. Take a hose to your cartridges (or is that a DE filter?) and see how it responds.

 

[launboy]

Yeah, but you could take your pool/spa suction valve and close off all suction to the pump and get the same problem. That doesn't mean it has to do with what causes it during normal operation.

Not necessarily, now I could be wrong in the way I'm understanding what was said, but when MSW said that covering the spa suction with the bag caused the vent to gurgle he(she) could have been talking about the inverted J vent. If this is the case, that would indicate a rather odd plumbing system(maybe some sort of redneck anti-vacuum device was put in by the PB that utilized a Spring loaded Check Valve) but you never know.

This is my other theory, that I don't even know is possible, but what if there was a suction leak underground and maybe a pocket around the leak. When the pump is off the water leaks out and fills the pocket then when the pump is turned on in the 30-40 min. the water gets sucked out then it begins sucking air.

Another thing you might want to try, that might rule out anything heater related.... You say the problem starts when the heater fires up for the second time, well, run it for the 30-40 min and when the heater would normally come on lower the temp or turn it off so it doesn't, but leave the pump running and in Spa mode.

My My, this is turning into quite the conundrum isn't it!

Adam