Toilet Siphons, Flush Valves and Weak Flushes
What is actually inside your cistern, and which part to blame for each misbehaviour.
Siphon or flush valve?
Older UK toilets flush through a siphon, which cannot leak water into the pan but can tire into a weak flush as its diaphragm wears. Modern dual-flush units use a drop valve, stronger flush, but the seal is the classic source of the silent running toilet.
Reading the symptoms
Needing two pulls: worn siphon diaphragm. Constant trickle into the pan: drop valve seal or scale on its seat. Weak flush with a healthy cistern level: scaled rim jets, especially in hard water areas.
Parts, not toilets
Every one of these is a replaceable part costing pounds. The skill is matching the mechanism to the make, which is why a photo of the inside of your cistern on WhatsApp gets you a faster fix than any description.