I have a quantum toilet that flushes normally but then syphons the water from the bowl Possible problem?

I am not familiar with the term flapper. I don't think our toilet cisterns use a flapper.

All the cisterns I have seen work by a syphon action and mostly the only thing that goes wrong with them is the thin polythene disc buried inside the syphon. The disc lays across a hollow piston and the linkage lifts the piston to begin the syphon action and the flush.

There are a few designs of push-button cisterns designed to be more economic on water which I haven't yet seen the inside of but I expect they too will work on a syphon principle - in the absence of a pump how else could it work?

in almost every case of a syphon not working (assuming everything is more or less as it should be) is air getting in somewhere and preventing the mechanism lifting the head of water to begin the syphon.

Sorry I can't help further.

Welcome to our new world of water conservation. If you have a toilet that isn't newer....you have something in your trap weir. Or your flapper is malfunctioning. Or your float valve isn't filling your tank correctly. Or your bowl scouring ports could be clogged. There are sooo many things that could cause this....
.New toilets do this because their design to use less water has reached the point of no-longer working to clear the bowl contents. Plain and simple. It has became the norm to flush once for #1's and flush (how ever many it takes to flush all waste) for #2's.
Back to old styles...You can remove the tank top and inspect the water level in the tank(should be about a 1/2" below overflow tube when full), inspect the flapper(flush the toilet and see if your flapper is staying up long enough to allow enough water to enter the bowl to cause a syphon action that ends with a suction sound and complete emptying of the water from the bowl), flush your toilet and look in the bowl to see if the water spraying from your rim is adequately dispensing water to scour the sides of the bowl, and also look at the jet that shoots water from the bottom of the bowl...aimed toward the outlet portion of the very bottom of the interior bowl. This jet is what starts the syphon action that empties your bowl. If you have something stuck in your trap weir....you probably need to call your Plumber to auger the object out or break it down to a size that will pass into the sewer.
The small ports that spray your sides can be cleared with a 3/16" stiff nylon brush...the jet down below can be cleared with a 1" stiff nylon brush. Flapper malfunction is repaired by replacing the flapper. Incorrect water level in the tank can be fixed by adjusting the valve float. but chances are that if it is all of a sudden malfunctioning...it probably needs to be replaced...good luck and always know how to turn your water off before starting work on your plumbing.
Be gentle with the parts inside your toilet tank. Using a calcium remover when clearing bowl inner ports and jets will help tremendously....but be certain to read the container and follow all handling/use instructions you read. Be careful.....Nick

i would think the syphon is not closing after the flush, so as the cistern fills it just runs straight into the pan. you'll need to replace the syphon...

Hi, if you remove the cistern lid and flush the toilet, look at the float (back left) to see if this is rising freely when the water fills back up. Once the water has stopped filling, check the fill level lines on the large syphon in the middle of cistern. Your model of toilet has an eco flush which will be lowest line to save water, so not as much water will flush out. There is a long plastic screw on the float (back left) which you can turn to adjust the water level to the higher line on syphon (1.6 gallon flush) and turn it slowley till the water level reaches that mark. flush a couple of times to see it is filling back up to the set amount.

It is normal for these useless new tanks to do that. Won't even flush a piece of paper. Pull off the lid and make sure the little hose is in the overflow pipe, and raise the water level as high as you can. take out all the bricks and water bottles, and bowl cleaners. Then give it a try. It might do a bit better. Hope this helps.

Adjust the float on the Fluid-master a little higher if possible. This should allow more water to enter the bowl after the flush.

Try holding the handel down for a couple of seconds each time you flush.

Sounds like your toilet is not vented properly. Possilbly something caught in the trap is causing it to syphon

make sure water level is sat at factory settings. there should be a black line that reads WATER LEVEL. If this is not the problem. then you have calci buildup. get a gal. of muratic acid,plunge all water out of toilet bowl. then dump in at least 1/2 gal. let set over nite. with water turned off. get up turn on water then flush. You mite have to do it twrice. hope this helps you.... duane.