OK, so I suppose the combi was a replacement for a system with HW cylinder, which would have involved pipework mods. Including some inappropriate ones!It definitely wasn’t original piping, there was a disgusting mix of pipe work, couplings, elbows under the floor, and lots of plastic and copper off cuts, so no idea what has happened under there, but at least it’s now resolved, and I got to crawl under my house which was kinda cool hahah
