Water randomly runs in toilet cistern!

Hi,
We have moved into a new rented property, and there is something weird going on in the bathroom!

Randomly, we hear a water pipe switching on at full flow for about 4-5 seconds and then clunks closed. I found one day that the noise was coming from the toilet cistern in the en-suite. It wakes us up in the early hours sometimes and I notice it happen maybe a couple of times each day.

The cistern sounds like it has filled up once flushed so I'm not sure what is going on. When we moved in we had low pressure in the heating system, this was corrected and the plumber said that the noise was air in the system being released.

I'm not convinced by the explanation - it sounds like water to me although I might be wrong.

Before I start taking it apart I wanted to see whether this is a common problem or likely cause?

The house is only 3 years old, runs on a worcester boiler and water tank in the cupboard upstairs.

it can be the flush valve in the cistern letting by and refilling that you can hear check to see if water is running into the rear of the pan.

seco services said:

it can be the flush valve in the cistern letting by and refilling that you can hear check to see if water is running into the rear of the pan.

Click to expand...

Hi, thanks for your note. No - there is no water flowing into the pan at all. I would remove the top of the cystern to have a look but it has been sealed and don't really want to make a mess. And equally still don't understand what would make it clunk a water flow randomly. Any other ideas?

I had exactly the same happening, just as seco says - A small piece of grit lodged on the flush valve seating caused very small, almost undetectable leak, hardly enough to wet the glaze, into the pan. It took a couple of hours for the water level do drop enough for the float valve to open to make up the difference.

The equilibrium float valves fitted in many cisterns tend to open fully for a few seconds and then snap shut when the loss is made up, where traditional float valves would hiss, wheeze and drip continuously.

Cleaning the flush valve seating cured the problem.