Odd leak from ceiling?

the problem sounds like it's the overflow leaking. I mean that your hot water unit sits on a safe tray so if your unit springs a leak the water will not leak inside the roof. Hot water also expands and there will be a pressure relief valve that will let the pressure out as the water heats up. You said that it started leaking after the sparky fixed the wiring he could have put his big foot on the overflow pipe from the safe tray and cracked the joint between the tray and were it exits through the eves. If you look out the bathroom window when it is leaking you may see the overflow dripping as well. It sounds like you have a gravity fed hot water unit which means the hot water is not pressurised the cold water enters through a cistern just like the one on your toilet. If you can follow me so far than you know when your loo keeps on running and you can bend the arm down and it will stop than this is what you may have to do to the hot water unit or the aspro washer may need changing. Call a plumber first he should be able to fix weather it's the hot water unit or a roof leak. Water damage will only get worse the longer you leave it so get it looked at asap.