Low pressure on cold tap

[cooperphilip]

In my nans house she has a gravity fed system with a water meter. She has a boiler which is not a combi for the radiators. No work has been carried out on the pipes all was fine then suddenly the cold water tap upstair has gone very low and sometimes stops. I put new taps on and then run the hot water up the cold pipe into the tank in the loft and there is no air lock. The pressure on the mains downstairs is fine so cant be anything to do with that. I also checked the tank in the loft to see if anything was blocking the hole to the feed but nothing there. Any ideas what else this could be ?

 

[dextrous]

The downstairs pressure (kitchen?) come directly from the mains supply and if the bathroom cold feeds from the tank, it will bear no relationship.

As for you efforts to use the hot water to shift an airlock in the cold water pipe, commendable as it is, it is flawed since there will be insufficient pressure to do so (both hot and cold water pipes will contain the same pressure regardless). It will be sufficient if you connect a hose to the kitchen sink and use this to clear the bathroom cold water pipework - more than likeley an airlock, but possibly a blockage which the mains pressure may dislodge.