Pressure Switch vs Pressure Controller vs Float Switch: Which Automatic Does Your Pump Need?

The right automatic for a water pump depends on what the pump is doing. A pump that fills a tank needs a float switch, because the water level should start and stop it. A pump that feeds the taps and showers directly needs a pressure control, because opening a tap should start it. For that second job you have two choices: the classic mechanical pressure switch with a pressure tank, or an electronic pressure controller, the blue or yellow box people simply call "the automatic", which needs no tank and adds dry-run protection. A float switch costs under $10 and an electronic controller $18 to $29, so the choice is not about money. It is about matching the device to the job, and checking one number on your pump before you buy the electronic one.

In this article

• What does each type of pump automatic actually do?
• Which automatic does a tank-filling pump need?
• Which automatic does a pump feeding the taps need?
• Why does the pump's maximum head matter with an electronic controller?
• Do you still need a mechanical pressure switch and a tank?
• When is an electronic pressure controller the wrong choice?
• When do you need a pump protection controller as well?
• FAQ

What does each type of pump automatic actually do?

Four devices get sold as "the automatic", and they sense four different things. Put the wrong one on a pump and it never starts, never stops, or burns out dry.

Device	What it senses	Right job	Needs a pressure tank?	Dry-run protection
Float switch	Water level in a tank	Filling a roof tank, emptying a sump	No	Only if a second float guards the source tank
Electronic pressure controller	Pressure drop to start, loss of flow to stop	Booster pump feeding taps and showers	No	Yes, built in
Mechanical pressure switch	Pressure only (cut-in and cut-out)	Booster pump with a pressure tank	Yes	No
Pump protection controller	Motor current and supply voltage	Guarding any single phase pump	No	Yes, from the current draw

A home with a ground tank and a roof tank usually needs two: a float switch on the transfer pump and, if the roof tank gives weak pressure on the top floor, an electronic controller on a booster pump.

Which automatic does a tank-filling pump need?

A float switch, and nothing else. The float hangs inside the roof tank on its cable with a counterweight clipped on. When the level drops the float tips down and closes the contact, the pump starts; when the tank fills it tips up and the pump stops. Sliding the counterweight along the cable sets how far the level falls before the pump starts. Wired the other way, the same switch empties a sump.

Read the rating before wiring a float straight to a pump. The WADFOW WPC2A163 is marked 16(4)A: 16 A is the resistive rating, and the 4 A in brackets is the inductive rating, the motor current the contacts can safely break. Check it against the amps on your pump plate. A small transfer pump sits inside 4 A; a bigger one should switch through a contactor or a pump controller that takes the float as an input, so the float carries only the control signal. On a two-tank house, a second float in the ground tank cuts the pump when the source runs dry, the only dry-run protection a float setup has.

The V.E.M. float switch at $3.58 does the same job; its page publishes no contact rating, so ask before using it on anything bigger than a small transfer pump.

Which automatic does a pump feeding the taps need?

An electronic pressure controller. It screws onto the pump outlet, the house pipe screws onto it, and the pump plugs into it. When you open a tap the pressure falls; as soon as it drops below the start pressure, 1.5 bar on the INGCO WAPS001, the controller starts the pump. When you close the tap the water stops moving; the controller senses the loss of flow and switches the pump off a few seconds later. It never stops on a pressure setting, which is why it needs no tank: the pump runs as long as water is moving.

The flow sensor doubles as dry-run protection. If the pump runs and no water arrives, the controller sees no flow and no pressure rise, cuts the motor and lights the failure lamp. Pedrollo's Presflo manual, a well documented controller of the same type, gives the family's figures: a shut-off flow of 2 litres a minute, start pressures of 0.8, 1.5 or 2.2 bar, and dry-running protection with automatic restart.

Controller	Start pressure	Max pressure	Max pump	Gauge	Price
INGCO WAPS001	1.5 bar	10 bar	10 A, 1,100 W	No	$29.00
INGCO WAPS002	1.5 bar	10 bar	Not published on the store page	Yes	$26.95
WADFOW WPC1A01	1.5 bar	10 bar	10 A	No	$21.95
V.E.M. Pressure Control Switch	Adjustable	10 bar	10 A	No	$17.91

The INGCO and V.E.M. controllers take a 1 inch pipe and are rated IP65; all of them run on 220 to 240 V single phase. The INGCO units are specified for water between 4 and 35 °C, so they belong on the cold line, never after a water heater.

Why does the pump's maximum head matter with an electronic controller?

This is the check most buyers skip. An electronic controller only works if the pump can push the pressure clearly above the start pressure. Pedrollo's manual puts a number on it: the maximum pressure the pump produces must be at least 1 bar higher than the start pressure. With a 1.5 bar start that means a pump rated for at least 2.5 bar, about 25 metres of head, at the controller. If the pump cannot get there, the controller reads the weak pressure as a dry run and shows a fault even with the tank full.

Height eats into that margin. Water standing in the riser presses down on the controller: Pedrollo's example is a controller 15 metres below the highest tap seeing about 1.5 bar from the column of water alone. The same manual pairs each start pressure with a maximum height for the highest tap above the controller:

Start pressure	Highest tap above the controller (Pedrollo)	Minimum pump max pressure (start + 1 bar)
0.8 bar	up to 6 m	1.8 bar
1.5 bar	up to 12 m	2.5 bar
2.2 bar	up to 20 m	3.2 bar

The INGCO and WADFOW controllers publish a single 1.5 bar start pressure, so by Pedrollo's pairing they suit a highest tap up to about 12 metres, roughly four floors, above the controller. Higher than that, the standing water keeps the controller above 1.5 bar even with the tap open, and the pump never gets the signal to start. Then mount the controller higher up the riser, or pick a controller with an adjustable start pressure such as the V.E.M. unit.

Do you still need a mechanical pressure switch and a tank?

Not for a new installation, but the old arrangement is not wrong, and in one case it is better. A mechanical switch has a cut-in pressure that starts the pump and a cut-out pressure that stops it. Because it stops on pressure, not flow, it must have a pressure tank in the line; without one, closing a tap sends the pressure to the cut-out instantly and the pump hammers on and off. The tank's few litres under pressure are its one real advantage: a toilet refill or a dripping tap draws from the tank and the pump does not start every time. Electronic controllers store no water, so a leak smaller than the shut-off flow makes them cycle; Pedrollo's troubleshooting table gives two fixes, repair the leak or add a small expansion tank after the controller.

An honest note on stock: we do not sell a standalone mechanical pressure switch or pressure tank at the moment. The classic arrangement comes built onto a pump instead. The INGCO VPA37068 at $64.95 is a 370 W self-priming booster supplied with its own pressure switch and a 2 litre tank, rated by INGCO at 32 m maximum head and 35 litres a minute; the DAFU DBT500 at $73.23 is a 0.37 kW automatic self-priming pump.

When is an electronic pressure controller the wrong choice?

• The pump fills a tank. Nothing closes the "tap" on a tank, so the controller never sees the flow stop. Use a float switch.
• The pump cannot reach start pressure plus 1 bar. Circulation pumps and low-head transfer pumps fault as dry running. Check the maximum head on the plate first.
• The top tap is more than about 12 metres above a fixed 1.5 bar controller. Move the controller up or choose an adjustable one.
• The pump draws more than 10 A or 1,100 W. Use a contactor between controller and motor, or a pump controller rated for it.
• Hot water. The INGCO units are specified for 4 to 35 °C. Fit the controller on the cold feed, never after the heater.
• Three phase pumps. These controllers switch a single phase supply only.
• A roof tank that already gives enough pressure. If the top floor shower is fine on gravity, a float switch on the filling pump is all you need.

When do you need a pump protection controller as well?

Neither a float nor a pressure controller watches the motor itself. The V.E.M. Intelligent Water Pump Controller at $29.85 does: it sits on the wall between the supply and a single phase pump of 0.37 to 2.2 kW, carries 15 A full load and 30 A at start, and trips on overload, a stalled motor, under-voltage and over-voltage. It detects dry running from the motor current, so it needs no sensor in the water, and it takes a float switch, level probes or a pressure switch as its start signal over a published 200 metres.

It earns its price on a pump that is expensive or hard to reach, such as a submersible in a well, and on any site fed by a generator or a weak line where the voltage swings. It also solves the float rating problem above, because the float then switches the controller's input, not the motor.

If you are still choosing the pump itself, start with our guides on which type of water pump a home needs and what size submersible pump a deep well needs, then browse the full pumps and motors collection.

Frequently asked questions

Does an electronic pressure controller need a pressure tank?

No. It stops the pump when the flow stops rather than at a set pressure, so there is no cushion to fill. The one exception is a system with a small permanent leak, such as a weeping cistern: the controller will cycle on it, and a small expansion tank after the controller stops that.

Why does my pump with an automatic show a fault when the tank is full?

Usually because the pump cannot push the pressure at least 1 bar above the controller's start pressure, so the controller treats the weak pressure as a dry run. Check the maximum head on the pump plate, check the suction for an air leak, and check that the highest tap is not too far above the controller.

Can I wire a float switch directly to the pump?

Only if the pump's rated current is within the float's inductive rating, the number in brackets, 4 A on a 16(4)A float. Above that, switch the pump through a contactor or a pump controller and let the float carry the control signal only.

What is the difference between a pressure switch and a pressure controller?

A mechanical pressure switch starts and stops on two pressure settings and needs a pressure tank to avoid hammering. An electronic pressure controller starts on a pressure drop but stops on loss of flow, needs no tank and includes dry-run protection. Both automate a pump that feeds taps directly.