problem flushing ideal standard dual flush (full flush)

[Aquaplumb]

Hello all, I've recently encountered a problem with a customers dual flush system. Its ideal standard, has a chrome flush plate with two buttons, large (full flush) and slightly smaller (half flush) The customer has two toilets within the property and both full flush systems are not operating correctly. I've removed the faceplate, two tubes are seen to connect to separate locking nuts on the pneumatic dual flush valve (SV05767). Ive removed the bellows washers but to the eye all looks fine with them. When i manually press the button beneath the bellows the flush works fine but when I reattach the bellows washer and press the full flush button on the face plate, it only partially opens, resulting in a weak, slow flush. Could the washers/bellows need replacing? the tubes look ok too, so Not sure what the problem is. Its like the air seal is lost. Can anyone suggest a possible or common problem with these?

Any help/advice is appreciated, thanks in advance!

[stevetheplumber]

your not folding the tube as you replace the lid ?

[Aquaplumb]

was carefull not to bend the tubes, so not that

[Aquaplumb]

oh ok, didnt see that, will check that one out thanks!

[stuartmac]

Hey there not expensive just replace them