Nobody's using water, and you hear the shower pump or booster pump kick on for a few seconds, stop, then do it again a few minutes later. Most people assume the pump is on its way out. Usually it isn't. It's doing its job, topping up the pressure because water is escaping somewhere on the system.
Quick answer
- Usually a leak, not the pump: a small leak lets the pressure drop, so the pump starts to build it back up
- The test: close the lever isolating valves on the pump's hot and cold outlet pipes. If the cycling stops, the leak is on the pipework the pump feeds
- Where to look: toilets passing water, dripping taps and shower valves, and the attic tank if the pump feeds it
- Still cycling with the outlets closed? Then it's the pump itself, and time to call a plumber
Watch: the isolating valve test that tells you if it's a leak or the pump.
Why a leak makes the pump cycle
A shower or booster pump, like a Stuart Turner Monsoon, senses when you open a tap, through a flow switch, a pressure switch or both, and runs until you close it. With everything shut, the pipework holds its pressure and the pump stays off.
If water is getting out somewhere, even a slow drip, the pressure drops. The pump sees that as a tap opening, starts, builds the pressure back and stops. Then the drip lets it down again, and round it goes. The troubleshooting guide in Stuart Turner's Monsoon manual lists a leak in the system (tap washers, toilet valve washers, pipe joints) as the first cause of a pump that cycles on and off with the outlets closed.
The isolating valve test
Most pumps have lever isolating valves on the pipes in and out. A quarter turn does it: lever in line with the pipe is open, across the pipe is closed.
- Close the valves on the pump's hot and cold outlet pipes, the ones going to the house. Leave the inlets open.
- Wait and listen for 20 to 30 minutes, or longer if the cycling was slow.
- Cycling stops: the pump is fine. The leak is on the pipework it feeds.
- Which side? Open the hot outlet only and wait, then try the cold on its own. Whichever starts the cycling again has the leak.
- Still cycling with both closed: the problem is at the pump. See below.
Open the valves again when you've finished. Nothing gets pumped water while they're shut.
Where the leak usually is
1. Toilets. A cistern passing water into the bowl is the most common culprit, and it's silent. Do the tissue test: wait 30 minutes after the last flush, dry the back of the bowl, then lay toilet paper flat against it. Wet within a few minutes means that cistern is leaking. A new seal or flush valve fixes it.
2. Dripping taps and showers. Check every tap the pump supplies, hot and cold. A shower head that keeps dripping after it's off is a giveaway. A new washer or cartridge usually sorts it.
3. The attic tank. If the pump feeds the attic tank, a ball valve that won't shut off keeps it filling. Check the overflow pipe outside, usually near the eaves. Dripping or running means that's your leak.
4. Pipe joints. Look along any pipework you can see, around the pump, cylinder and under sinks, for drips or damp patches.
Wet cold pipes under the kitchen sink too? That's usually condensation from the same hidden leak. Our guide to wet pipes under the sink walks through the same checks.
If it's the pump itself
If it keeps cycling with both outlets closed, the Stuart Turner manual lists the likely causes as a jammed flow switch, a faulty reed switch or circuit board, debris under the non-return valve, or low air pressure in the pressure vessel, on pumps that have one.
The vessel's air charge is checked with a tyre gauge, with the pump switched off, isolated and the pressure let off. The Monsoon Universal manual gives 0.9 bar for the 1.5, 2.0 and 3.0 bar twins and 1.3 bar for the 4.0 and 4.5 bar twins. Other models differ, so go by your own manual. Switches, valves and wiring are a job for a professional.
Don't leave it. A pump starting every few minutes, day and night, wears out far faster than one that only runs when you use water. Got a Tucson heating pump? That's a different pump, but check our post on the Tucson heating pump recall.
Common questions
Is it normal for a pump to run on briefly after I turn off a tap?
Yes. Many pumps have a short delay before they stop. It's the starting and stopping with nothing turned on that points to a problem.
Will a leaking toilet really make the pump cycle?
Yes, if it's on the pumped supply. A cistern passing water is a constant small draw, and the pump keeps topping up for it.
Do I need a new pump?
Not usually. If the cycling stops with the outlets closed, the pump is fine and fixing the leak is the answer.
What if I can't find the leak?
It may be hidden under a floor or behind a wall, which needs a plumber to trace. In Dublin and Leinster, get in touch.
Pump still switching on and off?
Our plumbers at CPS Plumbing & Electrical cover Dublin and Leinster, and will find the leak or fix the pump. Send us a short video of it cycling and a photo of its label, and we'll usually know where to start.
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