My water pump keeps clicking on and off. What is wrong?

A pump that clicks on and off has one of two faults, and when it clicks tells which. Calpeda, a pump maker with an office in Bangkok, splits them the same way: a pump that starts by itself while nobody uses water, and a pump that cuts in and out fast while a tap is open ².

A pressure tank tells the pump when to start

A pressure-tank pump, the kind sold as Mitsubishi WP or Hitachi WM-P, has a tank of compressed air, the ถังแรงดัน (thang raeng dan, pressure tank). A tap opens, the air pushes water out, the pressure falls to one mark and a switch starts the pump. The tap shuts, the pressure climbs to a second mark and the pump stops ¹. For Mitsubishi WP pumps, a dealer lists the two marks as 1.4 and 1.9 kg/cm² (kilograms per square centimetre, a unit of pressure) ⁶.

Clicks with every tap shut: a leak

A leak lets the pressure creep down until the switch starts the pump again, every 5, 10 or 30 minutes in Calpeda's example ². Hitachi's Thai site gives the same first check for a pump that cycles often: every tap shut, then a look for leaks at taps, pipes and the toilet ³.

Calpeda's test ²:

1. The gate valve on the pipe from the pump into the house is closed, for 1 to 2 minutes in the Mot Dang page's version ¹.
2. The pump stops: the leak is inside the house. Calpeda names the toilet's float valve, the bum gun (the spray hose beside the toilet), taps, the water heater, and pipe joints under the sink or above the ceiling.
3. The pump keeps clicking: the leak is at the pump, in the short pipe before the valve, or in a worn check valve (a one-way valve) that lets water run back.

A toilet leak shows with a few drops of food colouring in the cistern (the tank behind the seat): colour in the bowl with no flush means the float or the rubber flap leaks ¹. A leak inside a wall shows as damp marks, swollen or peeling paint, or drips from the ceiling ⁵.

Clicks fast while a tap runs: the tank has lost its air

A pump that runs a second or two, stops and starts again, mostly while a tap runs gently, usually has a pressure-tank fault, Calpeda writes. The common one is too little air: a small draw drops the pressure to the start mark at once, and closing the tap sends it straight to the stop mark ². With less air the tank holds less water, so the pump starts more often ¹.

The makers' fixes:

• Hitachi round tank. Toyobo, Hitachi's official Thai distributor, switches the pump off, closes the valves in and out, opens the plug under the tank until the water runs out, closes it and switches on. Toyobo describes the tank as half water, half air, and draining it as a reset. A pump still cycling after that may have a blocked air-intake part, for a new part or a technician ⁴.
• Hitachi square tank. With power and valves off, Toyobo shakes the pressure tank. Water leaking out means the tank has failed and is replaced ⁴.
• A tank with an air valve. Calpeda drains the system and pumps air in to the maker's figure, usually 2 to 3 psi (pounds per square inch) below the pump's start pressure. Water coming out with the air means the rubber bag inside is torn ².

A weak shower

Weak at one shower or tap: scale in the shower head or in the tap's aerator (the small screen at its tip), which unscrew for rinsing. Weak everywhere: a clogged filter cartridge, or more taps open than the pump can feed ¹. HomeGuru, HomePro's advice pages, names air in the pump as a common cause, cleared by opening the plug on the pump body and filling it with water ⁵. In a house on mains water with no pump, weak flow goes to the Provincial Waterworks Authority on 1662; its manual sets 24 hours for fixing weak or stop-start flow ¹⁰.

What to say to the plumber, and the prices

From the page's list of sentences. A woman ends them with ค่ะ (kha), a man with ครับ (khrap) ¹.

Prices read on 25 October 2026. HomePro's pump repair service is ฿900 for labour, parts extra, with a 90-day guarantee on the same fault; outside Bangkok it covers 40 km from a HomePro branch ⁷. A Hitachi pressure switch lists at ฿750 ⁸. A Hitachi nitrogen tank, the pressure tank for its constant-pressure pumps, lists at ฿1,500 ⁹. An independent Chiang Mai plumber's rate is unknown: the page found none published ¹.