Plumbing Advice – Trouble flushing your toilet

General Plumbing

Plumbing advice – for guidance only


more plumbing advice from your Hastings Plumber…


If you are having trouble flushing your toilet then it could be because the siphon inside the toilet cistern is broken. The first thing you need to do is to establish if you have a siphon in your cistern.

Remove the cistern lid. If the mechanism for flushing the toilet passes through this lid then you DON’T have a siphon, so there is no need to read on!

These instructions are for a ‘close coupled’ cistern which is the type where the cistern is mated to your toilet. If you have any other type then the principle is very similar so just make changes where needed.

You should see a square rod that passes from the flush handle through the cistern. There will be a lever arm attached to end of this rod and a metal wire that runs from the arm down to the plunger in your siphon.

Now that you have ascertained that you do have a siphon, we need to remove it. This can be easy, or in most cases difficult! Follow this guide to help you.

  • Isolate the water going into you toilet cistern. If there is no isolating valve on the pipe work leading to the filling valve, then you need to turn it off elsewhere and drain the pipe.
  • Next you will have to empty the cistern of water. Flush the toilet if you can or bail it out. You must get all of the water out.
  • Disconnect the overflow pipe from the cistern if there is one.
  • Now undo the back nut that joins the cold water pipe to the inlet valve. The inlet valve will either come into the toilet from the bottom of the cistern or from the side at the top. Do this carefully so as to make sure the water is truly shut off. It’s your last chance to avoid a flood!
  • Once you have removed the pipe, and you will get some water coming out which is trapped in the pipe work so have something ready to catch the water, you should loosen the filling valve where it passes through the cistern.
  • Reach under the bottom of the cistern and undo the two nuts, or wing nuts that secures the cistern to your toilet pan.
  • Remove the two screws that hold the cistern to the wall so that you can lift it off the toilet. Now drain any remaining water from the cistern and lay it on the floor or bench to work on.
  • Using a set of pump pliers unscrew the large plastic nut at the bottom of the cistern which secures the siphon and metal plate (if there is one). The siphon will now pull out from the top of the cistern.
  • Replace the siphon using a new 2 part siphon. It is more expensive but will save you all this trouble the next time the siphon diagram fails because it give you access to the diagram without going through all this nonsense!

Reassemble in reverse order, but it is wise to use a new ‘donut’ seal where the cistern mates to the toilet.

Be careful when you connect the cold water pipe to the inlet valve. You will remember that I told you to loosen the valve, and here is why. Usually the valve has a cheap nylon thread which the back nut from the water supply secures on to. If this inlet pipe is ridged then it is very easy to strip the nylon thread when relocating the back nut. If you have loosened the filling valve beforehand then you can move it and tilt it a little to offer up the back nut and make the first turn. Take note not to tighten the back nut just yet as you must first fully secure the inlet valve to form a seal with the cistern.

Now you are ready to do the final turns on the back nut to form a seal with the cold water inlet pipe. Don’t forget to use the fibre washer between the pipe and the inlet valve or it will leak!


PLEASE NOTE. These instructions are intended as a guide only. I can’t see the particular job you may be attempting so I can not give you definitive instructions. You undertake the work at your own risk and I accept no responsibility for the accuracy of these guidelines.