This is a WC with a high level cistern. It's worked fine for years but now it does this weird thing where about 50% of times after a flush it stops ... then starts sending gushes of water into the bowl. Sometimes is stops of its own accord other times it just carries on and you have to flush it again to make it stop. Sometimes in the night I go for a drink of water at the sink tap close by and it will start! The plumber said it was the siphon so we had it replaced a month ago but it still does it? What the hell is it? Tried reducing water pressure Tried making the cistern take less water - moving float stop down so it cuts off earlier. The plumber is also at a loss. Please can someone tell me what it is and how to stop it - its good and irritating!!