System blows out thru skimmer when pump stops.

Re: system backwashes immediately thru skimmer when pump sto

Does your Hayward sand filter have the side mount valve? If so there's an air relief cap on the dome top that you screw open a little to bleed the air off.
 
Re: system backwashes immediately thru skimmer when pump sto

Then it's not a 210S filter. It's most likely an S210T filter which has the SP714T valve. That valve is self venting and should vent air out of it slowly as the pump runs. You most likely have a suction side air leak and the vent isn't large enough to vent all the air out through the returns while it's running.

Does the pump basket have any air in it when the pump is running?
Is there any air coming out the returns when the pump is running?

Does the pump basket have any air in it when you're vacuuming?
Is there any air coming out the returns when you're vacuuming?
 
You are right, it's an S210T and I'll change the signature accordingly.

There is usually one or two small air bubbles in the top of the pump basket, which I assumed resulted from the shape of the lid (since it's curved upwards, it's really difficult to fill the basket to the top of the lid). Most of the time when I vacuum, air does come out of the returns.

I've had a visible water leak from the pump (dripping, not gushing) and yesterday the pool company came and replaced the ceramic seal. Since then air has been coming out of the returns and last night when I shut the pool off there was an enormous backwash burp.

Does a suction side leak mean that the pump will need to be replaced, or can it be repaired?
 
A suction side leak means air is being sucked in BEFORE the pump.

If it is happening especially when you vacuum, your vacuum hose is sucking air.

If it is still happening without the vac attached, it is occurring somewhere between the skimmer and the pump. Find and seal that leak(s) and your issue will be solved.
 
Are you cleaning and lubing the pump basket o-ring when you take it off and put it back on? That's a very common place for a leak. Also check the pump drain plugs and the inlet fitting on the pump. You can test the fitting by running water over it while the pump is running and looking to see if the bubbles lessen.
 
I lubed the o-ring earlier this year, but I'm guessing from what you write that I need to do it every time I take the lid off? That's an easy one to start with! I'll check the inlet fitting and the drain as well.

Is it likely that any of those three were removed/jostled when the pool guy replaced the ceramic seal yesterday?
 
but I'm guessing from what you write that I need to do it every time I take the lid off?
No, not every time at all...just make sure it is undamaged, lubricated and seats properly to give you a good seal.

If the situation got worse after the pump work, it is VERY possible they contributed to the issue but the leak WILL NOT be at the pump where they did the work....it'll be from the pump strainer basket back towards the skimmer....that's the suction side of your system.
 

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