Head Pump Problem

[karista]

Am experiencing a problem pumping water into the head. Water flow into the bowl is very weak. Replaced the cylinder, o-ring on shaft and seal! No improvement. Checked all the lines for blockage/restrictions--none found! Symptoms point to the fact that somehow I am pumping air into the line via the shower drain opening on the floor as I get a gurgling sound when pumping. This, drain line is hooked up to the shower drain pump, then its output side goes to a vented loop and out the thruhull valve, which also is the head water intake supply source. There appears to be a check-valve between the shower drain line and the pump according to the diagram, would its failure cause air to be sucked in by pumping water into the head? Any ideas?

[Ray & Sandy Erps]

I think you're on to the problem.  It's easier to suck air then suck water.  I'd pull the check valve out of the hose and clean it.  I'd also hold my thumb over the end of the line that goes towards the head and then see how well it draws in water.  I recollect our shower sump pump temporarily went kaput.  I closed off the through hull and drained the shower sump by pumping the head.

[John Gardner]

I think the valve is a non-return valve from the shower drain, to stop shower water flowing back into the shower tray from the higher line up to the anti-siphon valve.  Itwill allow water (or air) to flow from the shower toward the through hull (and potentially to the toilet) when it is working properly.  I think more likely is a blockage in the through hull (weed, plastic bag?).  What happens when you pump out the shower?  Does it go into the toilet bowl?  That would confirm a blocked through hull.  If you're lucky, it might clear the problem.

[Mike and Joanne Stimmler]

You might also try pumping the head with some water in the shower drain to see if it drains the shower. It might also clear the check valveif thats the problem.

[Ron Hill]

Try this : Turn off that thru hull - flip the toilet lever to wet bowl - turn on the shower sump pump and pour some water in the shower drain.  That water you poured should flow into the toilet bowl.  This will let you know that the line from the thur hull to the head is free and open.
As John mentioned the one way valve is to prevent back flow of shower water back thru the drain onto the head floor.  You might check to see if the antisyphon valve is seated properly.
Hope this helps?   

[karista]

Thanks for the ideas from everyone!
I had tried most if the recommendations, I disconnected the water intake hose at the head intake, lowered it below water level and had water gushing in, which means thruhull and line have no obstructions.  The sump pump works OK with the water being pumped out as it should. The check valve between the sump drain and pump is a one way valve as mentioned above, providing water flow to the pump but not back to the truhull water intake, thus I don't think its operation, if defective would have any impact. I do however hear a "hissing" sound when pumping at the vent loop valve, so I wonder if this could be defective and thereby letting me pump air in thru it. I will disconnect it and see whether this maybe the problem. Also , I may just disconnect the water drain line (from the sump pump) by installing a shutoff valve in its line at the drain end and see if this solves my problem.