What might be causing our cistern to fill very slowly?

Question

We have a toilet cistern with a concentric float valve fill mecanism. Earlier this week, it suddenly started to take much longer to fill after flushing (ca. 15 minutes instead of less than 1 minute previously). Simultaneously, the sound produced by the filling became a much more noticeable hissing sound.

Inspecting it wasn't much help, as I'd not really looked at it before it went wrong. I did notice that the hissing sound is caused by water emerging from the top of the fill pip at pressure. That, combined with normal operation of other water outlets, leads me to believe that the problem is isolated to the cistern.

What might have gone wrong? Is there a simple fix? Or will I have to call a plumber?

Answer 1

Some dirt or sediment is probably in the valve within the toilet itself. Here's a video of the repair on two types of valves. The important part is to get the valve opened up, clean off the washers, run a little water through the system, and reassemble.

Answer 2

First thought is some kind of clog in the line/fill mechanism.

Easiest and quick solution there is to shut off water to the toilet, drain the tank by flushing, then put a pan under the fill line and remove the bottom end first (disconnecting it from the shutoff) allowing the remaining water to drain out the tube into the pan.

Then remove the other end from the toilet and flush the line with water in the bathtub, reconnect both ends, and turn the water on again.