Repair of a slowly-refilling toilet
I've replaced the float-valve mechanisms in toilets many times, but the most recent one had me baffled for a long time. It regulated the water level in the tank, as expected, but the toilet bowl didn't refill to the expected level, and the tank took way too long to refill. I never timed it exactly, but it was probably on the order of 20 minutes. We tolerated that for a long time, and I just couldn't come up with a theory to justify action.
The low water in the bowl problem turned out to be a pinched tube between the float-valve and the refill pipe. That was easy to fix. I took the "pinching mechanism" off entirely.
Eventually, I decided that there must be a foreign object of some kind in the water line. I had a pin-hole leak repaired, and thought that maybe, somehow, the plumber who fixed that had created the problem. So, I shut off the water, drained the tank, removed the float-valve, cupped one hand over the open water line (where the valve had been), and cautiously turned the water back on. I got plenty of water (to mop up). So, the problem was in the float valve. I looked up into the tube, and saw something that didn't seem to belong. I pulled on it with a pair of needle-nose pliers, and it turned out to be a threaded chunk of white rubber. I guess some mischievous employee at the factory poked it in there. As soon as I re-assembled the valve, the tank took two minutes to refill.
No parts charge. No labor charge. No personal injuries! (that's not to be taken for granted, the way I work). No trips to the hardware store. Just taking a few minutes to think through the possibilities, and devise an experiment to test them.