Pump primes well only when backwashing


Apr 18, 2018
Hey all! I have a bit of a strange problem.. I have an in ground pool, with a Triton tr100 sand filter and an old pentair style pump. I have the main drains turned off and have a drop in conversion to utilize a 4 wheel Poolverneugen (Hayward) Pool Cleaner vacuum with the little baby skimmer door.

The pump seems to prime well only when backwashing. When it kicks on to clean the pool with the water set to return to the pool there is barely any suction. But then if I shove down the backwash valve, let it spool and prime, theres plenty of suction at the skimmer/ in pool cleaner. Sometimes when I return the Valve to the normal position it keeps on sucking, sometimes it goes back to barely any suction at the skimmer/vac side.

Any suggestions? The old pop up system is functioning as my returns if that's relevant. Also the pump doesn't sound ultra healthy but it's a Dang workhorse. For the last 4 years I've had people say "oh those bearings are on their last legs from the sound of it" and the thing keeps on trucking. I was considering getting it rebuilt before the season really kicks off.

Thanks so much!!


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TFP Guide
Jul 3, 2013
Southern OK
It sounds like you have a slide valve on your TR100... When was the last time you deep cleaned your TR100? it could have blocked sand in there and needs to be broken up... Could also have blocked fingers that need replaced but if they were broke I think you would have some sand returning back to the pool..

When you say the pop up system do you mean the pool cleaning pop ups.. do you have a way to bypass them? something may be wrong with it..

What is your PSI when running?