Leak via overflow pipe- picture inclided

[TheGander]

This is in my brother’s home, he’s been away for months due poor health and we went back last week to prepare for his return home. I had turned off the cold water at the stopcock and on turning it back on water started gushing out from the overflow pipe. It’s an old hot water system with a tank in the loft. As can be seen there is serious limescale deposition around the float valve. Also, the ballcock is behind the end of the float valve. My question is can this be fixed by me, maybe by moving the ballcock down the shaft so it sits lower and turning it round so it is at the end of the valve’s arm. Or should the whole float valve be replaced?

That water is disgusting. No lid on the water tank? I'd empty that out before anyone uses it to brush their teeth!

Ball cock and valve should be adjustable. May need lubricating or replacing.

This doesn’t look sanitary. Definitely get it sorted before your brother returns, that can’t be healthy.

You’re right it is disgusting, as is the whole house- about 30 years of hoarding and mental illness in there 😞. It’s a huge task getting it back to a functional state. Thanks for the advice.