My shower has been leaking continuously since I bought my house, through the ceiling below into the kitchen leaving a stain on the kitchen ceiling. Its in the corner of the bathroom with 2 tiled walls and 2 shower enclosure walls. I tried having a plumber friend having a look at it. He poured water down the drain and this didn't cause a leak so he said it wasn't a problem with the pipes. I resealed the edges of the walls and along the base of the shower inside and out but the leak continued. The drain became blocked recently and filled the base of the shower while I was showering and when I came downstairs afterwards the leak was so bad there was water on the countertops and floor of the kitchen. I've also always had problems with limescale and have had to replace my shower once already. Do you think these issues are related?

Pouring water down the drain doesn't check everything. It sounds like water is either leaking around a worn out seal in the bend under the drain, or leaking around the top edge where plumber's putty or a gasket might have worn away. I would have suggested checking for a leak inside the wall too, at the showerhead or control, but you say it was worse when the drain backed up.

I would cut out a neat square of ceiling below, middle of the joists to make patching easier, to look at your drain.
You could just clear the blockage in your drain first if you want to take the easiest approach first, since you should do that anyway. Sometimes water flows right past a spot that will only leak when it's backed up.

And buy a hair trap for $2 to help prevent future blockage.

Stop by hardware store and get a 1/2' threaded PVC pipe cap. Remove shower head. Screw pipe cap onto end of shower arm. Cap needs to be installed reasonably tight but it does not matter if it leaks a little. Turn on shower. Wait for 30 minutes. Check for leaks.

If leak occurs you have a leak in water supply pipes. Probably where shower arm screws into pipe inside the wall. Pull escutcheon around shower arm away from wall and with flash light look in side wall for signs of water. If you have an access panel on the other side of the wall that has the shower valve remove the access panel and look for signs of water. If you do not have a access panel, remove shower valve handles, valve stem covers and escutcheons. Look look inside wall for signs of water.

If there is no leak while you have the pipe cap installed get a flat rubber drain stopper and put over shower drain. Using a bucket and water from another source, fill the shower base with about 2" of water. Check for leaks. If no leaks get in shower and walk around. Check for leaks. If you have a leak you have a cracked or leaking shower pan. If no leak occurs while you have the shower pan filled with water, remove the drain stopper. If leak occurs while water is draining you have a leak in drain piping.

If none of these things make the leak occur you will have to start looking for leaks through tile walls.

What type of showers do you have? Custom built tile or plastic base and enclosure? Do both showers leak or just one? N Did your plumber friend block off the drain and fill the base with a inch or so of water to check the drain seal? Back to you, Tom

It's a plastic base and electric shower. I have another shower over my bath and this doesn't leak... as far as I know anyway! He didn't fill the base, just suggested I reseal the shower.

Let's find out exactly where your leak is. If the shower floor flexes or gives a little as you step in to it that would indicate that the base was never bedded in at installation. This puts a strain on the drain seal and in time will rupture it. Let's find out for sure, Remove the strainer from the shower drain and jam some wet rags down there to close off the drain. Now run a inch of water in the base and watch the ceiling for any moisture. If you see new moisture let the water out of the base and get back to me where I'll give you instructions on how to reseal the drain. I'm assuming you have a plastic drain like the one I've pictured (see image). Good luck and let me know. Tom