Well Pump Not Building Pressure? 7 Checks to Find the Cause (Winter Guide)
Turn on a faucet in January and get a trickle, or watch the gauge sit at 20 PSI while the pump runs and runs. A well pump that won't build pressure is one of the most common calls we get once the weather turns cold. The good news: most causes are simple to find, and many are fixed with a part, not a whole new system. This guide walks you through the checks in the order a pro would do them.
Safety first: turn off power to the pump at the breaker before you touch any wiring, the pressure switch or the plumbing. If you are not comfortable working around 230V, call a licensed well contractor.
Step 1: Read the pressure gauge and listen
Note three things: the pressure when the pump kicks on (cut-in), where it stops climbing, and whether the pump ever shuts off. Most home systems use a 30/50 or 40/60 PSI pressure switch. If the pump starts at 30 but stalls at 35–40 and never reaches 50, the pump is not producing enough pressure. If the gauge swings fast between on and off, skip to the waterlogged tank section below.
Step 2: Check for frozen or cracked lines (winter only)
In cold snaps, the first suspect is ice. A frozen suction line on a jet pump, or a frozen pipe between the well and the tank, will starve the pump. Look and feel along any exposed pipe in a crawlspace, pump house or well pit. Signs of a freeze include frost on the pipe, a pump that hums but moves no water, or a split pipe or cracked pump casing after a thaw. Warm the area slowly with a space heater or heat lamp (never an open flame). If the pump casing cracked, it needs replacing; see our frozen or cracked pump guide.
Step 3: Jet pumps: lost prime or a suction leak
Shallow well jet pumps such as the Goulds J5S, J7S and J10S need a solid column of water on the suction side. If air gets in, the pump loses prime and pressure falls off. Common causes:
- A leaking foot valve or check valve that lets water drain back down the well.
- A loose fitting or cracked pipe on the suction side (look for wet spots or a hiss).
- The water level in the well dropped below the reach of a shallow well pump (roughly 25 feet of lift).
To re-prime, shut off power, remove the priming plug, fill the pump and suction line with water until it overflows, replace the plug and restart. If it loses prime again within hours, you have a leak or a bad foot valve.
Step 4: Worn impeller, diffuser or seal
Jet pumps that have run for years, or that pumped sand, wear the impeller and diffuser. The pump still runs, but it can't push water to full pressure. A leaking shaft seal also shows up as water under the pump. For Goulds J-series pumps, a rebuild kit replaces the wearing parts for far less than a new pump: J5S/J5SH rebuild kit, J7S rebuild kit, J10S rebuild kit.
Step 5: The pressure switch
A pressure switch with burnt or pitted contacts, or a clogged sensing tube, can cut the pump off early or keep it from reaching cut-out. With power off, remove the cover and look at the contacts. Clear the small tube under the switch of rust or sediment. Switches are inexpensive and a common wear item; browse pressure switches.
Step 6: Submersible pumps: wear, voltage or a hole in the pipe
For a submersible pump down the well, low pressure usually means worn pump stages, a split drop pipe or a failing check valve, low voltage, or a weak control box capacitor on 3-wire systems. A hole in the drop pipe often shows as the pressure bleeding off slowly when no water is in use. Control box parts are a cheaper first check than pulling the pump: see submersible control boxes. If the pump end is worn, you can often replace just the pump end and keep the motor.
Step 7: Don't forget the filter
A clogged sediment filter after the tank looks exactly like a weak pump at the faucet, while the gauge at the tank reads fine. If tank pressure is normal but house pressure is low, change the cartridge first.
Quick diagnosis table
| What you see | Most likely cause |
|---|---|
| Pump hums, no water, cold weather | Frozen line or pump |
| Pressure climbs then stalls below cut-out | Worn impeller/diffuser, suction leak, low well level |
| Pump runs, loses prime overnight | Foot valve or suction-side leak |
| Fast on/off cycling | Waterlogged tank or wrong air charge |
| Good pressure at tank, weak at faucets | Clogged filter |
FAQ
Why does my well pump run but not build pressure?
The pump is moving some water but not enough to reach the cut-out setting. The usual causes are lost prime or a suction leak (jet pumps), worn internal parts, a split drop pipe (submersibles), or a frozen line in winter.
Can I keep running a pump that won't shut off?
No. A pump that runs nonstop overheats and can burn up the motor or melt plastic fittings. Shut it off until you find the cause.
Should I rebuild or replace my jet pump?
If the motor runs smoothly and the casing isn't cracked, a rebuild kit is usually the better value. If the casing is cracked from freezing or the motor is failing, replace the pump.
How fast can I get a replacement?
Many Goulds J-series pumps usually ship within 1-2 business days. Ship times can vary with supplier stock; call (866) 202-8388 to confirm before you order.
Need a hand? Call our pump team at (866) 202-8388 (Mon–Fri, 9 AM–5 PM ET) or email help@supremewatersales.com with your pump model, well depth and tank size. We will tell you what fits before you buy, no obligation.