In my early days as a player, the only maintenance advice I got was to soak my instruments in beer, often from those who had already soaked themselves. I resisted. Just as well, my Marine Band combs would have suffered.
Maintenance with the older harmonicas was hit and miss, with no guidance. The instruments, held together with nails, were hard to get apart, hard to get back together. All this has changed. Basic harmonica maintenance is now straightforward, the right tools easily gotten. If you've not yet rolled up your sleeves, now is the time.
The most common problem is a note refusing to sound. Excess spit is often the cause. Bang the instrument against the heel of your hand several times, then breathe in and out rapidly over the offending hole.
Better? No… Then something is lodged in the reed. First, we locate it. Hold the harmonica in your left hand, with the lower notes toward the heel of your hand (the normal playing position). Then find the blocked hole. Count if need be. If the blocked note is a draw, then the associated reed is the one adjacent to your thumb. A blocked blow note means the reed is closest to your forefinger.
Having found the blocked reed, push against it gently with a wooden toothpick. Move the reed slightly, in and out of the slot (I did say gently). This may do it.
If not, then a key harmonica ritual comes next: removing the cover plates. Take a small Phillips head screwdriver, and undo the screws on each side. A standard screwdriver will be too big, get a set of small ones from your hardware store. Do this work on a table, place the screws carefully in a cover plate, located so that you don't bump it. Losing the screws in a carpet is a classic own goal. Remain scoreless.
Now look at the blocked reed. Sometimes a small nose hair is the culprit, pushing the reed out gently will remove it. All should then be well. One nil.
Replace the cover plates, making sure that they are the right distance from the top of the comb. If you have another harmonica of the same brand, then use it for a reference. It's easy for the cover plates to go back on too high, making the instrument harder to play.
If the problem is the two draw (second hole, breathing in), and you are a beginner, chances are that nothing is wrong with the harmonica. This note is the bane of new players, and also the fundamental blues note. Google "two hole draw", you'll find help.
Another common problem is a note which sounds, but jams at higher breath pressure. Here the "gap", or the distance between the reed tip and the reed plates is too small. This gap can be widened, again by pushing the reed out of the slot several times with the wooden toothpick. For draw reeds you can see the slot width, for blow reeds you can't, as they are on the inside of the instrument.
Another common problem is a reed which suddenly goes way out of tune. Bad news here. The reed has cracked at the base, and either it, or the harmonica needs to be replaced. Most go for the latter. With steady playing, a harmonica should go at least 6 months before a reed goes bad. Modern harmonicas seem to last much longer than the older ones.
The next step is a harmonica repair kit. Here I'll hand over to the experts. Tombo (Lee Oskar) have long had a basic harmonica toolkit, Seydel now have a comprehensive range, available on their site. Harmonica customiser Richard Sleigh has a good toolkit, available on his site. Hohner have taken big steps forward in recent years, with a complete range of harmonica toolsets and parts. Better still, they have an excellent series of maintenance videos, showing how to set reed gaps, tune reeds and replace broken ones. The videos are here.
So. Next time some lazy money heads your way, buy a harmonica toolkit. Then get an old harmonica, watch the Hohner videos, then try setting the reed gaps, using the proper tools. Correct gapping greatly improves harmonica performance.
A final maintenance topic, mentioned in passing only (I'm out of words), is reed tuning. Fairly straightforward. Filing/scraping metal from the top of a reed raises the pitch, removing metal from the bottom of the reed lowers the pitch. Again, watch the videos, use the right tools, practice on an old harmonica.
Basic harmonica maintenance is just that. The skills and tools to keep your instruments running are now easily had. Get them, practice a little, then thank me down the track.