WiremanWireman · Float or pressure switch pump control: troubleshooting for electricians · 2023 NEC ·
Float or pressure switch pump control
Pump won’t start, won’t stop or short-cycles: check the switch, then what it’s sensing.
Before you start
How much electrical experience do you have?
This sets how much detail each step shows. You can change it any time.
Showing detail
How it works
A float or pressure switch is just a switch that a level or pressure operates. A pressure switch on a well opens at cut-out pressure and closes at cut-in (the setting is printed inside the cover, for example 40/60 psi). A float closes on rising or falling level depending on whether it’s a pump-down (empty a pit) or pump-up (fill a tank) type. The electrical side is simple. Most trouble is the switch’s contacts or what it’s sensing: a stuck float, a clogged pressure port, or a tank problem that makes the pressure swing too fast.
Every question and answer in this guide. Tap “Step by step” to walk through it.
- What is the pump doing?
- Won’t startTest: Measure across the switch contactsExpect: Supply voltage on the line side, and near 0 V across each closed pole.
- No supply on the line sideNo power reaching the switch
- Full voltage across a poleIs the switch actually seeing the condition?
- Float stuck or pressure port cloggedThe switch isn’t sensing the real level or pressure
- Condition is right, switch still openFailed switch contacts
- Low-pressure cutoff trippedThe low-pressure cutoff tripped
- Switch closed, pump still offThe switch works; check the pump circuit
- Won’t stopWhen the tank is full or the pressure is at cut-out, is the switch open?
- Switch never opensLook at the switch with power off. Are the contacts welded, pitted, or full of insects or debris?
- Contacts welded or burnedFailed switch contacts
- Contacts look fineThe switch isn’t sensing the real level or pressure
- Switch opens, pump keeps runningSomething else is feeding the pump
- Pressure never reaches cut-outThe pump can’t build pressure to cut-out
- Switch never opensLook at the switch with power off. Are the contacts welded, pitted, or full of insects or debris?
- Turns on and off rapidlyShort-cycling: usually the tank or the switch differential
- Won’t startTest: Measure across the switch contactsExpect: Supply voltage on the line side, and near 0 V across each closed pole.