Water Tank not filling

My next door neighbour dropped by this evening to see if we were having problems with our water which we weren't. Nosey as i am I went into his house to have a look. The water was coming in at tap downstairs but his tank wasn't filling in the attic. He was away for a few days over Christmas and that heat wasn't on but I wouldn't have thought the pipes were frozen or anything. they didn't seem too cold. Any suggestions? Any solutions?

Could be low pressure from the mains. Happens sometimes but usually for a short time, but this would effect you also.

Probably the ball cock (spelling?) is stuck (metal lever bar with a plastic ball at end). Push this up and down a couple of times to see if the water starts to flow.

Same thing happened to myself last week. It was indeed the ballcock. (Spellcheck says one word)

If you look into the tank, you should see that it's stuck on something (central tube thing) or it's broken.

Make sure you know where the shutoff valve for the tank is before you wiggle the ballcock (just in case it's broken!).