Hello But of a puzzle. I was away and my partner called and said 'there's a small leak'. She lives in an old 1880s terrace that's been broken up into shop (ground floor) and 3 flats..hers is the top flat. She has a combination fitted..an old Worcester 24i. But there is a coldwater tank in the loft..big old thing..poly (not metal). That's where the leak is coming from...partner has BG home cover and an engineer came out..'not the combi'..then a plumber..'it's your coldwater tank...it's not the overflow leaking though...old coldwater tank, somehow leaking from coldwater tank but hard to tell' I arrived back and took a look. Here's where it gets a bit odd. There's a coldwater tank in her flat but she's got a combi boiler??? I always thought that when the combi and central heating was fitted that they just couldn't be bothered to remove the it...so just left it. So I thought..drain coldwater tank, remove ballcock, replace with stopscock and then connect to the 4 exit pipes that seem to supply the bathroom cold, then chop up and remove coldwater tank and re route the 2 mystery over flow pipes that are directed into the top of the present tank into the overflow pipe that runs through the slates onto the roof. I turned off the stopcock in the bathroom..that stopped cold supply going to the sink, bath and toilet cistern...I tied up the ballcock to stop it filling the cold water tank and drained the tank...thought I'd leave it til Monday before I did anything else....then the tied up coldwater ball cock loosened enough to refill the cold tank to just above the 4 exit holes and, coincidentally or not??.. suddenly one of the mystery overflows started to flow with cold water. Got to thinking maybe the cold water tank supplies the flat downstairs....so went downstairs and the guy is trying to repressurised his immersion tank!! He can fill it from the mains but there's also a mystery (to him) pipe teeing off and going somewhere...the cold water tank in my Gf's loft. ...and the overflow passing water is him trying to repressurised his tank...and presumably the other mystery overflow is the shop/ the other flat's immersion heater.. It's a right dogs dinner Is the best/ easiest solution to replace the massive old failing cold water tank with a new one quarter the size? ...or something more 21st century?