Fluidmaster siphon not working?

[Anakin]

So I’m called out to fix a toilet that isn’t flushing. It is a concealed cistern within a box.
When you press the button, the flapper comes up a tad without flushing. The outlet of water then pushes the flapper right up and does not sit back down again, so continuously flows into the pan. Pressing the buttons does nothing, nor does playing with any of the slide adjustments do anything either.
So I get a new siphon, thinking it has to be busted within the preset factory wire to the button. No change whatsoever! Frustrated I then try a second, and third siphon - still the same.
The flush pipe isn’t blocked, and water does flow freely into pan. Now I’m aware this was a new install via builders - being that they’ve boxed and tiled everything. The owner is going to speak with them as this being in a 5 storey conversion into flats. My theory is there is no vent, so no vacuum which is preventing it working. Could this affect the flush in this way, or have I just been really unlucky with three brand new siphons? One being from different suppliers.

 

[Brambles]

Assuming that this is an air operated push button / lever syphon. Are you sure that the air line is leak free, properly connected and the bulb in the button / lever is being fully compressed.

The above of course assumes that you have only replaced the syphon each time and not the pneumatic controller

 

[Riley]

Also don’t know how you think a vent would work here?

 

[townfanjon]

Longshot , is the cable on a smooth run , ie no kinks or bends ?

 

[Burger]

Have you tried it “dry”? As in out of the cistern to make sure it works or to see why it doesn’t?

 

[Aire]

As above, if cable operated, does the cable have a smooth curve to it to ensure correct operation. If pneumatic then check hoses, for splits, kinks etc. Also are you changing the whole syphon or just clipping one out and new one back in? Could be some fault with the original installation causing the plunger to stick open.

 

[Ben-gee]

From your description it is a cable operated flush. Detach the cable from the flush valve and make sure it operates correctly.
This sounds like a kinked Bowden cable to me.
If it works ok then carefully attach it to the flush valve and it should be fine.
If not replace the button and cable mechanism.
You’re not getting it kinked as you reassemble the boxing are you?

 

[Anakin]

There are no kinks or out of character bends on the cable. Tried replacing the entire mechanism, and different buttons although they all identical. All the siphons work perfectly when dry. Add water and they have a hissy fit

 

[Riley]

Are they siphons or dumpvalves any chance of some pictures

 

[Anakin]

 

[townfanjon]

Blimey I have fitted loads of them , if you ever find out the problem please re-post

 

[Ben-gee]

Are you sure you’re connecting the button to the cable correctly?

 

[Riley]

Was gonna say button is pressed valve lifts. Is there a chance that it’s not seated in the cradle properly

 

[Burger]

If it’s dual flush, have you set the sliders correctly? You could be getting a very short flush? Tried contacting fluidmaster technical helpline?

 

[Anakin]

Ok so sorted it. On closer inspection when not dripping with sweat in a small enclosed cupboard bathroom with no window, the cistern although level, was leaning forward at the bottom about 20mm ish. So at a slight tilt. In theory it should work fine, clearly it did not. I’m guessing that the stopper do dabs didn’t like the bit of tilt, so didn’t sink back down.
I refitted a different brand siphon, (can’t recall which) and made sure the bottom of cistern was straight as could be. Bingo worked right away. No more screwfix concealed cisterns, or fluidmaster siphons for me! Note had to get new 2 inch flush pipe which reduced to 1 1/2, and get a new nut and washer. Multiple brands of siphon didn’t have long enough thread for the nut to tighten! Ah well

 

[Ben-gee]

Glad you got it sorted.
They do seem quite fickle some of these dump valves.
I have quite a few customers asking me “to get rid of the silly button flush” and put in syphons after years of poor performance and lots of maintenance- we do have hard water here.