Beeping, one long, two short

Had the same issue. From what I can tell, it was telling me the toothbrush was still on while it was charging. (The battery died mid-brush.) I turned it off while on the base (don’t know if that matters) and the beeping and flashing lights stopped. Hope this helps.

Solved and verified: what this beep pattern actually means

The repeating pattern (one long, two short, three short – easy to mis-hear as "one long, two short" since it loops without a clear starting point) is not a malfunction beep of the charger and not a defect signature of the electronics. It is a defined firmware status message meaning: the power button is being held down / stuck while the handle is on the charger. For those who do morse code: it's "TIS", obviously referring to "This is $@$*".

I verified this experimentally on a Sonicare ProtectiveClean: after repairing the switch (see below), with everything working normally again, I deliberately held the power button down while docking the handle. The exact same pattern played in a loop and stopped as soon as I released the button.

Why does this happen without anyone touching the button? The most common cause is moisture inside the power button's tact switch. These SMD tact switches are not hermetically sealed – water creeps in through the gap around the plunger. A thin water film (or the mineral residue it leaves behind) bridges the contacts, so the firmware sees a permanently pressed button. The full symptom chain on my unit: power button unresponsive while mode button worked fine, brushing cycles spontaneously restarting ~38 seconds after each cycle ended, and this beep pattern whenever the handle was docked.

The fix, with the internal assembly removed from the housing:

Using a syringe with a needle, place a few drops of isopropyl alcohol right at the gap where the switch plunger enters the switch body. Capillary action pulls it inside.

Immediately press the switch rapidly 20–30 times – this pumps the IPA under the contact dome and dissolves the residue.

Repeat two or three times, flushing generously on the last pass so the dissolved residue is carried out rather than redistributed.

Let it dry for an hour or two in a warm place, then test.

Plain drying alone often only helps temporarily: the water evaporates but leaves conductive/hygroscopic mineral residue on the contacts. The IPA flush removes it. If the switch still shows continuity across its contacts when not pressed (compare with the intact mode switch as a reference), the corrosion is established and the switch needs replacing – a standard SMD tact switch, cheap and solderable.

And the obvious prevention: don't keep the handle in the shower. The spray mist entering along the drive shaft is exactly how the water gets in.