Help please not sure how to fix this back boiler issue

[Grankin]

Hi i have an old back boiler in a ground floor flat. The expansion tank is in the bedroom cupboard and above it is a black tank that is full of cold water with a ball cock in it. This has been making a constant runing water sound for a week and i have only just noticed the overflow outside is pouring out. I opened the lid of the tank and its full to the overflow valve and just keeps filling. I am guessing the hot water feed is in my upstairs neighbours loft. What do i do to fix this will it be the ball cock or something else? Should i turn the water mains off? Is this safe over night or will it possibly overflow out the tank?

 

[Chuck]

Try gently lifting the ball cock a couple of millimeters. If the flow stops you may be able to rest a piece of wood (if you have one) across the top of the tank and use a piece of string hold the float up until morning.

If that isn't feasible (or the gentle lifting doesn't do the trick), turn off your water at your stopcock over night.

Don't apply excessive force to anything and particularly not at this time of night.

If it's not your flat contact the landlord of agent to get the problem fixed. If it's your flat I recommend you employ a plumber.

 

[Harvest Fields]

Definitely your ball cock. You can just change the diaphragm on some of them. Have you got a picture of the valve. But be careful not to drop your phone in the tank