Is your toilet 'chugging' as you try to flush it? Your siphon / syphon more than likely has a torn diaphragm membrane, this is quite a cheap and easy fix for most brands currently on the UK Market.
If you are unsure on what brand you have, you can check our previous guide here: identifying-your-toilet-flush-valve
One of the most common brands currently installed in most cisterns is Macdee by Wirquin, their products can be found from Scotland to Ireland in different range of colours as over the years as they have updated their branding, but it is 100% the same syphon.
Please note you must ensure it is the three part type with removable nut, as you will be required to split the cistern if not.
You'll need to follow the steps below:
Currently their syphon comes in four distinct shapes. Square, Oblong, 'D' Shape & Round, to fix the 'chugging' issue all you need to do is match the membrane shape up to your current siphon shape via the ones on the link below:
Remove the nut attaching the siphon to the stem (you shouldn't need to turn the water off or split the cistern for this step), pull out the C hook, and remove the cradle from the bottom before replacing the worn washer.
Your toilet should now flush as good as its first day.
Should you be unable to source the washer for your syphon or are tired of replacing them a couple of times a year you can always replace it with the universal Motion by Macdee, that has rigid lower plastic flaps.