Gravity Fed Cold Water supply

[Fatcockney]

I have an issue in an upstairs en-suite and separate bathroom, where the cold water supply to both has gradually ceased over the last week. Both areas have showers which have loft based power mixers and these are working fine.

if I put the showers on, they both take water from the cold water tank in the loft. If I flush the toilet or use the sink basins in the same room there is absolutely nothing.

Any ideas please would be gratefully received.

Regards

 

[Nige F]

Dead rat/bird in the cold cistern in the roof - blocking the outlet OR the powered showers are taking water faster than it's replenished causing an airlock in the other feeds