Check nothing is in the valve blocking it and the fact its opening fullyour house is 5 years old and has had a new internal in the main bathroom cistern.
It’s really slow to fill now but not always. Any ideas where to look please chaps
Or somebody occasionally drawing a lot of water upstream of your property?Don't be surprised if the water board have been round and turned down all the outside stopcocks to reduce the flow into the house as it happens to mine regular