The pump that starts and stops every few seconds: the pressure tank's air charge and the valve

A pressure pump switching itself on for three seconds every twelve is not being busy - it is drowning in its own job, because the cushion that should let the system breathe has gone soft, and every dripping tap or half-seated flush is now a start command. Left alone, the cycling grinds the pump's life to months, bangs the pipes until joints loosen, and the desk's first sentence is the good news: the two usual causes are a ten-minute check and a part cheaper than the call-out, with one boundary - the pump head itself stays closed.

The two symptoms, because they share a cause

• Short-cycling: the pressure system works by squeezing air in a small tank (vessel) while water runs into it; the air - compressible, patient - feeds the house between pump runs, and the switch tells the pump when the pressure band is done. When the air cushion is gone (the tank waterlogged, the bladder inside it burst) there is nothing between the pump and the tap: pressure snaps up, the switch cuts, a tap moves, pressure snaps down - the machine starts again, forever. The knock test the trade uses on the tank itself tells you which half is guilty: a vessel that sounds solid-full of water at every angle has lost its cushion.
• Waterhammer: the bang when a solenoid closes - the washing-machine valve, the flush - is the same missing cushion telling the pipes to ring like struck fencing; the air spring absorbs the stop, and with nothing to absorb it, the pressure wave throws the pipework. The banding the pipe straps and the loose joint it fatigues start as the noise and finish as the leak.

The evening's own sequence, up to the line

1. Find the ghost draw: with everything off in the house, watch whether the pump still ticks on a cycle - a slow creep means a leak downstream (the cistern's silent flush, the garden tap, the ballcock that never quite seats; the tank-overflow guide's paragraph on the float is the same fix from the other end), and a no-traffic cycling with the lines still is the pump's side of the fault.
2. Isolate and test the vessel: the power off, the system pressure bled to zero at an open tap, the tank's air valve checked with a bicycle-type gauge - if it reads nothing where the system wants a starting figure, the recharge is the air pump and five minutes of this page's whole household-accessible repertoire (the correct pre-charge number is printed on the pump's or vessel's own label; the desk publishes none because every model runs its own band). A valve that spits water when pressed is the bladder's death certificate, and the part replacement is priced by the pump's model, not by this page.
3. Then the non-return: the little valve that keeps the suction line full between runs - if the pump has to re-prime every start, air in the line explains both the dry-tapping start and the house's upstairs losing pressure first when several taps run; the valve lives where the pipe meets the tank or bore line, and its replacement is the plumber's thirty-minute job the desk will not dress up as a tap-wrench errand for the wrong-handed.

The boundary, printed straight

Inside the pump head is a professional's room: the pressure switch's contacts, the capacitor, the impeller wear that shows as a pump that runs long and builds pressure slow - all are the electrician-or-pump-service conversation, and the 'adjust the switch screw' video is how houses end with pumps that never cut off and a burst line. The same paragraph covers the borehole itself: if the draw-down test says the source is thinning (pump runs to pressure, then the flow weakens as the well recovers slowly), the fix belongs to the pump-size conversation with the well's driller - cycling a dry bore is how a household pays twice.

The quiet prevention tier

The vessel keeps its air when the system is not asked to run bone-dry (the tank's minimum-level switch the overflow guide already preaches protects pump and bladder together); the taps and flushes get fixed when they drip - each one is a start signal over the cushion's lifetime; and the loose pipes get strapped (a pipe clip screwed home tight stops the banging that loosens the joint costing the wall). The desk files short-cycling as the system's polite complaint: the bill arrives at the motor only if the polite version is ignored.

The desk's standing rule

Tap off, watch the cycling, knock the tank, gauge the air - the four-step evening that names the fault in the two cheap parts; and the fifth sentence that stays true whatever the fix: the head itself stays closed, because the pump that is repaired wrong is the water that stops arriving quietly, six weeks later, with a bigger invoice.