jfgw wrote:Boilers do not have overflow pipes.
What does the pipe look like? If it is copper and pointing back toward the wall, it is the outlet from the pressure-relief valve. This is the water that runs through your radiators and is about as corrosive as rain water.
Julian F. G. W.
Julian - I went to the apartment today to take photos of said 'overflow' and position of downstairs' Flue - - and sure enough, you were right - what I had seen as an 'overflow' pipe [and described as uPVC] - is in fact a dinky copper pipe that points back to [almost touching] the wall. So it is outlet from pressure-relief valve. [Ground Floor say they 'heard it dripping at 4.00 a.m. one morning in early January. Not sure why the system would let water through at that point, as my Mother had not used the boiler / heating / hot water at all until we got Vaillant out 10 days' ago. But anyway.] The good news is your info that the water in the radiator system is non-corrosive - - so I do not see what claim the Ground Floor can make against my Mother. If it is virtually 'ordinary water', that makes the 'drip' from that outlet no more serious than heavy rain. Which there was a lot of around the time they say their boiler developed the problem. Thank you so much for your help, Julian.