The previous post and some of the comments got me to thinking about what I will and won't do, technology-wise.
The trade-offs are time, skill, tools and trouble. We needed a new garbage disposal last week; I hired it done. It's not that hard to replace the things and it'll save almost $300, but I was very busy with work and it is a royal pain wrestling 'em into position; I paid a plumber to do it. For other plumbing, it depends on the pipe; all the half-inch copper accepts those nifty push-together fittings. There's some plastic pipe with crimped fittings in the system, though, and I don't trust it nearly as much. I'll probably end up paying a plumber to change out critical bits to copper, when it needs it, and finish it up myself.
I paid an electrician to install new receptacles in my bedroom and the washroom, plus a vent fan in the latter. I could have done it but I don't like opening up a panelboard when I'm by myself, plus he did a much neater job than I could have. On the other hand, I had to point out where he could install the new breakers by removing an unusable range circuit.
On my MGB, I would do everything but adjust the carburettors and valves and major engine work. The first takes experience to do well and the second, well, the procedure is insane, not to mention messy; the tiny engine has to be warmed up, shut off, valve cover yanked and everything set quickly before it cools off; a really cautious mechanic slaps the valve cover back on and has you drive it around the block after he's got halfway so it stays warmed up. I let the shop (gone now and much missed) change it over to electronic ignition, too. (The old distributor conked out and that particular version wasn't available -- they had several different curves for the vacuum advance, to match the carb needle valves. Electronic retrofits can fake it). On the other hand, I've installed new gas tanks and gauge sending units, thermostats, a clutch master cylinder, even changed out a driveshaft U-joint and replaced the front disc brake pads and flexible lines. Newer cars, I'm done at plugs, filters and driveway oil changes -- and it is so much easier to drive through for the latter now.
So it depends. But I still think one ought to at least know enough to see if the hired help is doing a good job or not.
A local HVAC outfit managed to put themselves on my "never hire" list when I was buying this house. On inspection, there was a crummy so-called permanent filter in the furnace, gummed up and flapping in the airflow, too small for the opening. The inspector and I requested it be changed to a proper-sized pleated filter and sure enough, the seller had his long-term HVAC guys do that and included the receipt in the paperwork, showing the work had been done. The first time I went to change the filter? You guessed it. The very same lousy filter. They'd done nothing. And been paid for it.
The basics are not that complicated -- hot on the left, cold on the right and drains run downhill; live wire is the narrow blade, black wire; neutral is wide blade, white wire; ground is the green or bare and the U-shaped pin.* Flues gotta connect, filters need to be tight all the way round and if you can't see light through them, they're probably toast. Reader's Digest turned out a "home handyman" type book and it (or a similar tome) is worth owning even if you never do any of the fixing yourself, because it will tell you how the fixing should be done. You don't need to be an expert, you only need to be able to read and to think -- and to know what your own limits are.
* Unless you don't happen to live in North America. Elsewhere, if you are lucky, you'll find the new "universal" color coding: hot wire is brown, toasty brown; the neutral is blue, cool blue; the ground or earth wire will be green with a yellow stripe. But older homes? Could be anything, check your local codes and practices and ditto on how to wire up sockets. UK and Commonwealth counties with 220-240V mains may find red for hot, black for neutral and clear for earth but do NOT take my word for it. Adjacent countries used the same or similar colors for different functions; way back when, they didn't compare notes and there were only so many colors available. The U.S. practice of using white for neutral supposedly comes from electricians marking the return wire with chalk back when black rubber and cloth insulation was common.
6 hours ago