In wall cistern mystery?!

[rh2205]

We had a roper Rhodes in wall cistern installed in 3 bathrooms, one of the 3 just won’t work when the flush plate is on (been like this since water turned on) all the parts have been replaced and it still stops flushing after maximum 5 flushes, seems to get stuck, it works perfectly when the flush plate is hanging off the wall, anyone heard of such issues?! Think we’ve had the plumber round 5 times now, I was wondering if it could be the proximity of cistern to the wall which would obviously involve cutting walls out, any other ideas as to why something so strange would happen? All the other toilets work perfectly but the cisterns are set deeper in the stud walls elsewhere & the plumber really has no clue.

[rh2205]

Should add it’s a pneumatic flush https://www.roperrhodes.co.uk/u/products/downloads/TR9009_In-Wall-Cistern_TDS_V1_190503_110312.pdf 

 

[ProDave]

Could it be one or both of the pipes kinks when the flush plate gets put into position thus blocking air flow?

[markc]

41 minutes ago, ProDave said:

Could it be one or both of the pipes kinks when the flush plate gets put into position thus blocking air flow?

I was thinking the same as it seems only logical reason but you would think the plumber would have checked before or while replacing parts.

[rh2205]

If it is a kink how do you stop these pipes kinking? There is nothing obvious when you take it off so it must be something occurring at the very last inch of putting the flush plate on, again nothing when you remove it, it must be a very marginal snag/kink if it’s that,  takes about 5 flushes before the flush buttons no longer work, works instantly again once you remove flush plate and press the buttons. He also thinks it’s very strange & has never come across an issue like this, he had been hypothesising that it’s because the plastered wall is slightly bowed & maybe that is somehow causing an issue. I might try it tightened up to some packers to see if the cistern is just set too close to the plate, from what I can tell the cistern is directly behind 12mm plasterboard on a un tiled wall, it’s not obvious there is a gap, thus if this is the case could it be as simple as the 20mm distance to flush plate hasn’t been met (of course no one would admit this & I can’t remember what the build up behind looked like so this is just my theory).

[Nickfromwales]

Replace the pneumatic pipe and try again. I had this before and it was a series of micro-fractures in the pipe allowing air to escape when the flush button ( basically a set of bellows ) was pushed. Swap the pipe off one of the working ones to see if the problem migrates to the other WC.

[dpmiller]

tiny leak. each time pushes a wee bit of volume out of the pipe til there isn't enough to send the signal