Toilet refilling when neighbour flushes!! All aspects of plumbing questions and answers, help, tips and information

[trainee laydeee plumb]

Hi wonder if anyone can help? My friend lives in a flat, and everytime the flat immediately below hers flushes their toilet, it syphons the water out of her toilet cistern! Then her cistern has to refill. She had a new bathroom fitted a couple of years or so ago, with a new close coupled toilet, and that's when it started-never happened before then. She says she had a plumber out last year, who said he'd fixed it (I think he may have changed the flush valve from what she's described), but it's getting worse. Any ideas?? Thanks in advance.

[plastic_man77]

@ trainee laydeee plumb

Look in your toilet cistern and see whether there is an air break between the inlet valve and the water level (There should be one)- and whether the water level has been set correctly.

Also, there must be a case of low water pressure in the pipework feeding both your toilet and your neighbours. Try and improve this if possible (Check external and internal stop cocks are fully open and that the internal one isn't partially blocked- or if fed from a storage tank, make sure the feed isn't restricted in any way, such as a gate valve not being fully open).

To prevent any futher siphoning of used water, possibly in to the mains depending on your pipework configuration, fit a non-return valve as close to the cistern inlet valve as possible.

[trainee laydeee plumb]

Brilliant cheers, I'll give it a shot.
I think the flats are mains fed (flat roofed purpose built flats-can't figure out where they'd put a loft tank), but it def could be water presseure. My mate said she'd only had this problem since new toilet put in, and it's got worse since a plumber came to look at it. Could the problem be stemming from downstairs? Is it worth checking to see if they've had any work done?

I'll go round and have a look/fiddle with it and let you know :-)