The siphon unit that is fitted in the cistern for the toilet uses the downward pressure of the water that sits in the full tank to keep a seal (rubber) in tact. The unit will sit inside your WC and when required will make it flush (as stated with the downward water pressure) by lifting and dropping a large rubber seal over a hole in the base of the WC cistern. The rubber seal can sometimes wear or it develops bubbling. Either of these could be to blame for a failure leading to a leak, or, it could be down to debris that is sat in the cistern. Radlett Plumbers can repair or fit a new siphon. The debris in the cistern is usually the remnants of the water freshener blocks that are placed in the cistern.


If you suspect the siphon has failed, then:

1). Isolate the water supply and flush the water away.

2). Remove the cistern and remove the top of the siphon by turning and lifting it off. Sometimes there are clips are fitted, if so press them in and remove the siphon. The design of these does vary.

3). Once removed, turn the siphon over and visually inspect the rubber seal on the base, looking for bubbling. If it looks damaged, then replace it with a new one from your local plumbers merchant. Take the old unit with you to get the correct replacement. The new one will probably need to be ordered so keep the old one for now. If the rubber looks fine, then check for debris. Clean out the cistern as a matter of course. A Radlett Plumber would carry out this action. Fir the top of the siphon back on the base, either twisting or clipping as necessary.

5). Restore the water supply and visually check that the unit is nowleak free. If you couldn’t replace the seal straight away and the toilet is still leaking a lot of water, then isolate the toilet until a repair can be done.