A pressure tank isn't just a storage vessel — it's a shock absorber. Inside is a bladder with a cushion of compressed air. When that cushion is gone, the pump has nothing to push against, so it starts and stops constantly.
How to check it yourself
Turn off power to the pump, drain the system, then check the air valve on top of the tank with a tire gauge. The reading should be about 2 psi below your pump's cut-in pressure — typically 28 psi on a 30/50 system.
If water comes out of the air valve, the bladder has ruptured and the tank needs replacing.
Why it matters
A healthy system lets the pump run at least a minute per cycle. A waterlogged tank can push that down to a few seconds, meaning tens of thousands of extra starts a year. Motor start-up is when the wear happens, which is why short cycling shortens pump life so dramatically.
Repair or replace
If the bladder is intact and the tank has only lost air, recharging it solves the problem. If the bladder is torn or the shell is corroded, replacement is the only real fix — and it's far cheaper than the pump it would otherwise take with it.