I cut myself by ignoring Occam’s Razor

Occam’s Razor states that, all other things being equal, the simplest explanation is to be preferred. I wish I’d remembered that this afternoon.

We have just completed a major landscaping/hardscaping project – and as long as the driveway was being dug up, we decided to replace the 50-year-old galvanized pipe between the water meter and the house with brand new copper. The replacement went well, but after the plumber had left, I noticed that one of my toilets was refilling very slowly.

I ignored it for a couple of weeks, but finally I was irritated enough to Google the problem: “Fluidmaster 400A slow refill”. The top page in the results came from Fluidmaster, and it suggested several causes:

  • After several years of use, the seal of the 400A fill valve can become swollen, causing a slower fill.
  • The inlet of the valve or the water supply line is plugged with debris.
  • For new installations, if using a straight pipe as a water supply line, it may be extended too far inside the bottom of the valve shank.
  • For new installations, the valve cone washer may have been used with the wrong supply line.

This wasn’t a new installation, and the toilet was only a couple of years old, so I was pretty sure that debris was involved. Fluidmaster suggested removing the top cap from the valve and using the water pressure to clear debris from the valve. 30 minutes later, I’d finally managed to remove the top cap, only to discover that there wasn’t much pressure. Their explanation for that was “debris lodged deeper in the valve”, but trying to fix it would require draining the tank and getting water all over the floor, which I wanted to avoid, so I searched further.

HandymanWire gave me a great tip to replace only the top part of the valve (avoiding any need to drain the tank and get water on the floor), so I followed their procedure. 10 minutes later, I had the valve disassembled, ready to put on the top part of a new valve. But for some insane reason, I decided to test the pressure before putting the new valve’s guts on…and there was no pressure.

I drained most of the water from the tank and disconnected the hose leading to the tank. Then I cleaned up the water on the floor (oh, well) and turned on the water – still no pressure.

I disconnected the other end of the hose, right by the angle stop, and found a small pebble blocking the hose inlet. Removing the pebble solved the problem, and then I spent the next 20 minutes putting everything back together, including putting the old guts back on the valve.

In retrospect, the simplest explanation was a blockage in the water supply line – just as Fluidmaster (and Occam) suggested. If I’d tried that first, I would have been finished in 10 minutes (even with cleaning up the floor) — instead, I spent about 2 hours (including research and a couple of interruptions).

Oh, well; now I know a lot more about the insides of a Fluidmaster 400A valve than I did this morning.

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One Response to I cut myself by ignoring Occam’s Razor

  1. Robert Clagett says:

    David, we did the same thing.. Yard and Copper pipe from the meter.. best move ever.. you probably see it on your walks.. Doing the pipe means the nice yard will not have to be dug up when the old pipe breaks.. oh, and the higher pressure is nice too..