Why is my pump turning on and off
Most of the ones we get called out to have a leak in the system, not a faulty pump. The fastest way to prove it is to fit a valve at the outlet of the pump, shut it, and watch.
If the pump stops cycling with that valve shut, the leak is downstream in the property. If it keeps cycling with the valve shut, the problem is at the pump, its controller, or its non return valve.
The short answer
Fit an isolating valve on the pump outlet if there is not one there. A ball valve and two fittings. Power off and pressure off first.
Let the pump run up and stop, then shut the valve and leave it half an hour.
Goes quiet, the leak is in the property. Still cycling, the fault is at the pump end.
Why does a pump turn on and off by itself?
A pressure pump has one job: hold the water in your pipes at pressure. It starts when the pressure drops and stops when it comes back up or the flow stops. That is exactly what it should do when you open a tap.
So when it starts and stops with every tap shut, something is letting pressure out. Either water is escaping somewhere, or the pump cannot hold what it has just pumped. The valve test tells you which, in about half an hour.
Cycling is a symptom, not a fault. Find where the pressure is going before you buy anything.
The valve test, step by step
-
Fit an isolating valve at the pump outlet
If the discharge side of your pump has no valve on it, fit one. It is cheap, and it makes every future service easier because you can work on the pump without draining the property. Switch the pump off at the isolator and let the pressure off the line before you cut into any pipe, and get a plumber to do it if you are not confident. Never work on the wiring, the terminal box or the controller yourself, that is registered electrician work.
-
Let the pump run up and stop, then shut the valve
The pump, its tank and its controller are now sealed off from the property, provided they all sit on the pump side of the valve. Check that first, because some installs have the pressure tank teed in further down the line. Nothing past the valve can affect the pump once it is shut.
-
Watch it for fifteen to thirty minutes
Run no water and flush no toilets. Just listen, and note whether it starts and roughly how often.
Result A
The pump goes quiet
The pump end is holding pressure. Water is escaping out in the property, fast enough to drop the pressure and wake the pump up. Start with the toilets.
Result B
It keeps cycling
The fault is at the pump end. Pressure is getting away back through the non return valve, the foot valve or the controller. A flat pressure tank will not cycle a sealed system on its own, but it makes any leak cycle far faster, so check it too. Work through causes 2, 3 and 4.
Cause 1: a leaking toilet or trough valve
This is the hidden leak we find most often, and nobody suspects it because there is no puddle to stand in. A cistern outlet valve that does not seat leaks straight down the back of the pan, day and night. The only thing it shows up on is the pump.
The dye test. Put a few drops of food colouring in the cistern and do not flush. Come back in twenty to thirty minutes. Colour in the pan means that toilet is leaking through. Do every toilet, one at a time.
After the toilets:
- Trough and tank float valves. A float valve that is passing draws water constantly. Common where the pump also feeds stock water.
- Outside taps. Check every one, including the ones round the back you never use.
- The hot water cylinder relief valve. A little discharge while the cylinder is heating is normal. A valve that runs or drips constantly is a leak like any other. Leave the valve itself to a plumber and never plug or cap a relief line, it is a safety device.
- Buried pipe. Look for a wet patch, a soft spot, or a green strip in dry weather. If you have valves out in the paddock, shut sections off one at a time and repeat the test.
Cause 2: the pressure tank is waterlogged or the precharge is wrong
A pressure tank holds a cushion of air behind a rubber diaphragm. That cushion is what lets you draw a jug of water without the pump starting. Lose it and the pump has nowhere to store pressure, so it starts and stops on the smallest draw.
Waterlogged tank. Press the air valve on the tank, the same type as on a car tyre. Air should hiss out. If water comes out instead, the diaphragm has split and the tank needs replacing. Domestic tanks are sealed units, so it is a replacement, not a repair.
Precharge too low. Air pressure in a tank drops slowly over the years. Check it with the system depressurised and the tank drained of water, and set it to the figure in your pump manual, which sits just below the pressure the pump starts at. Too low and the pump cycles rapidly whenever a tap runs.
We stock Davey Supercell pressure tanks and the pump parts and accessories that go with them. If you run a variable speed pump the rules are different, so check your manual first. Some, like the Davey DynaDrive and the DAB E.SYBOX, have a small vessel built in and need nothing added. Others, like the Davey EvoDrive, have no built in tank, and a small bladder tank can help settle short cycling on very light draws.
Cause 3: the non return valve or foot valve
A non return valve lets water go one way only. It stops what the pump has just pushed up the line running back down again. When it fails, pressure bleeds backwards, the pump sees the drop, and it fires up to make it good. Then it does it again.
On a suction lift setup, with the pump sitting above a tank or a creek, the foot valve at the bottom of the suction line does the same job and holds the prime. A leaking foot valve gives two symptoms: cycling, and a pump that has lost its prime by morning.
These are cheap parts, but a valve buried in a bore head or under a tank is a bigger job than the part price suggests.
Cause 4: the pressure controller
Electronic controllers such as the Davey Torrium2, Grundfos PM PLUS and Grundfos PM Start start the pump when pressure drops and stop it when flow stops. Most contain a small non return valve of their own.
When a controller plays up you usually get fast cycling, every few seconds rather than every few minutes, sometimes with the pump hunting up and down while a tap runs.
Do the valve test before you condemn the controller. Controllers get blamed for a lot of leaks that turn out to be a toilet.
What the symptom is telling you
| What you see | Most likely cause | What to do |
|---|---|---|
| Cycles with no taps on, stops when the outlet valve is shut | Leak out in the property | Dye test the toilets, then troughs, taps and relief valves |
| Keeps cycling with the outlet valve shut | Non return valve, foot valve or controller | Check the tank air valve, then call us |
| Water out of the tank air valve | Diaphragm split, tank waterlogged | Replace the pressure tank |
| Rapid on and off while a tap runs | Precharge too low, or a controller fault | Check precharge with the tank drained |
| Prime lost by morning | Foot valve or suction line leak | Check the foot valve and every suction side joint |
Do not just leave it cycling
Every start is wear on the motor and the starting components. A pump that short cycles all day runs up far more starts than it was built for, and left long enough it can cost you the pump.
On tank water there is a second bill coming, because whatever is leaking is emptying your tank as well.
Found the leak but cannot fix it today? Switch the pump off at the isolator between uses.
When to call us
Plenty of this you can do yourself. The valve test, the dye test, checking troughs and taps, pressing the air valve on the tank. None of it needs a tradesman, and all of it narrows the job down.
What you do not touch is the electrics. Do not open the terminal box, the controller cover or any wiring, do not defeat an RCD or a thermal cutout, and do not run a pump on a lead you have made up yourself. Wiring a pump is registered electrician work, and a pump sits in a wet place where getting it wrong kills people. Switch the power off at the isolator before you touch the pump at all.
Call us when the pump keeps cycling with the outlet valve shut, when the tank is waterlogged, when you suspect the controller, or when anything electrical is involved. Same for bore pumps, because the pump itself is down the bore and pulling it is our job, so once you have checked the tank, the wellhead valve and the controller there is nothing more to do from the surface. We sell and install house pumps and bore pumps around Waihi and Thames every week.
Talk to us
Tell us how often it cycles and what happened when you shut the valve. That is usually enough for us to tell you what you are up for. A real person picks up.
65 Kenny Street, Waihi, Monday to Friday 8 to 5. 74 Kopu Road, Kopu, Monday to Friday 8 to 3.
