Replaced WC syphon to no effect.........

GRC · 6 Dec 2004

I've just given someone a hand to replace the syphon in their WC - fault symptom was that the flush handle needed to be 'pumped' to get the WC to flush. Conventional wisdom suggests that the flap at the base of the syphon, which gets lifted by the flush handle, wasn't forming a good seal to the side of the syphon and hence failing to lift enough water to start the flush.

Away we went to the plumber's merchants, got an identical replacement, installed it, and at the first flush; got EXACTLY the same symptoms. I checked the conditiion of the flap prior to fitting it, and it looked good, and when operated in the dry, sounded good as it dragged along the side of the syphon wall.......... but it still takes a couple of 'pumped' pushes of the flush handle to get it to go.

What am I missing here?

Regards, Graham

corgiman · 6 Dec 2004

how is the water level, if its too low you will need to pump it

kevplumb · 6 Dec 2004

check the pan where the water enters as well can be restricted

corgiman · 6 Dec 2004

that will affect the out flow of water kev, I thought he was having probs getting the syphonic action going.

I could be mistaken, believe it or not it has been known

kevplumb · 6 Dec 2004

i fell for this once if the water cant get out fast enough the syphon cant

GRC · 6 Dec 2004

Thank you, chaps;

The water level in the cistern is fine, filling up OK to within a centimetre or so of the overflow level.

The delivery rate to the pan also (when we did get a full flush) seemed OK, fairly seemed to tumble out there..... however if we do de-cistern it again, we'll have a go at probing the waterway for blockages; the installers had gone for the belt & braces approach when assembling the original - silicone sealant around the thread at the syphon base, a generous wodge of it around the donut as well........ the donut was a bit decayed, so possible some of that could have fallen off and got stuck.....?

Regards, Graham

kevplumb · 6 Dec 2004

wasnt a syphon with the holes in the side ?
if so did you blank the right ones off ?

MANDATE · 6 Dec 2004

Could be the original plastic membrane has become detached and is causing restiction, or has this been accounted for when old unit removed.

kevplumb · 6 Dec 2004

good point mandate

GRC · 6 Dec 2004

The original membrane was still present on the old syphon - well turned up at the corners, but apparently still whole and not with any missing pieces.

Regards, Graham

GRC · 6 Dec 2004

The new one IS a syphon with side holes, but since they are purely to vary the volume of the flush (i.e. to break the syphon effect when the remaining water reaches them) I wouldn't have thought they would have an effect on getting it started; they are all under water when the cistern is full...

Regards, Graham

brumylad · 7 Dec 2004

Is the water able to flow past the membrane ok, is the membrane somehow jammed closed against the top of the housing at the end of the flush.

leafy · 7 Dec 2004

Perhaps the lever isn't lifting the membrane high enough - adjust linkage.

GRC · 7 Dec 2004

With it being a new syphon, it has a good strong spring return, and looked as though it was returning to the base of the syphon no bother.

Also, travel of the membrane is far enough to actually move the body of the syphon as it and the plastic frame hit the top of their travel...

Regards, Graham

MANDATE · 7 Dec 2004

I know you say the water level is almost at the overflow pipe, but I'm wandering how much of the syphon is protruding above the water level.
If the water level is well below the top of the bend, then there may not be sufficient volume of water moved to start the syphon. The higher the water level the easier it is to start the syphon. I suggest a simple experiment. Plug the overflow pipe with finger, depress float and increase water level by say 30mm. Now flush.
I increased the height of my overflow pipe by 30mm and the water level by the same amount, which meant the syphon pipe had smaller volume of air and required smaller volume of water to get syphon started.
It does make me think there is nothing standard about heights of syphons, cisterns and overflow pipes.

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Replaced WC syphon to no effect.........

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