One Line Jet Pump (C) Daniel Friedman Diagnose Weak Water Pressure Water - Table 3 of 3
Troubleshoot water pumps that run but don't deliver enough water or weak water pressure

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This WATER PRESSURE PROBLEM DIAGNOSIS TABLE series provides a table giving step by step checklist for diagnosing water pressure, water pump, and water well problems. We give diagnostic and repair procedures for both municipal water supply problems and well water supply problems.

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Diagnose Poor Water Pressure or Weak Flow Rates Delivered from a Water Pump & Well System

Don't give up.

Table 3: Well Pump Runs but Does Not Deliver Any Water or Does Not Deliver Enough Water

Closed or partly closed water supply valve Be sure that you haven't forgotten and left a valve closed between the pump and water tank. This can happen if someone closes a valve to perform other work on the plumbing system. Be sure at least one clear water piping pathway is open between the water pump outlet side and the water pressure tank inlet side.

Low Well Water Level or Loss of water in the well

If the well water level has fallen too low or the well recovery rate is too poor, or if the well pump is oversized for the well flow rate, the pump may run continuously.

Turn off the well pump and allow the well to recover - one to several hours may be needed.

Re-start the well pump. Note how much water can be drawn before the water supply or flow rate drops or stops.

Other symptoms of this problem include air discharge at plumbing fixtures.

Install a properly-sized well pump matched to the well flow rate.

Install a tailpiece and/or low water cutoff device to protect the pump from damage.

Switch from a shallow-well (one line jet pump) to a deep well equipment system (2-line jet pump or in-well submersible pump).

Investigate and fix the cause of a poor flow rate or low-yield well.


Low Line Voltage - slow pump operation


Use a VOM to check the line voltage at the pressure switch or pump motor wiring terminals

If the voltage is under the recommended voltage (see pump label or installation manual) check that the wiring is of proper gauge for the amperage and length of run.

Confirm that voltage at the electrical panel is normal

Partial loss of pump prime


Air in the pump or piping system may reduce water flow. See AIR DISCHARGE at FAUCETS, FIXTURES

If no water is being delivered and the pump is running and it's an above ground pump, turn off power and inspect the pump cavity for the presence of water by removing the priming plug.

If the pump is a submersible unit in the well, loss of prime is not normally an issue.

A bad check valve or failed foot valve can lead to loss of well prime.


Re-prime the pump - see

If the problem is recurrent see

Water piping problem: undersized or clogged water pipes

Water pressure is weak in all building areas or only in some building areas, but at some or all fixtures in that area.

If water supply piping is too small in diameter, or if there are many, perhaps unnecessary elbows and fittings, especially if there are long piping runs in the building, water flow will be impeded.

If water pressure is consistently poor regardless of pump settings, or if when you turn on water the pressure is strong for a moment or two, then falls off quickly you may have clogged piping or under-sized piping.

Install larger diameter water supply piping in part or all of the supply system. Installing larger piping in even part of the system will help.

Check for & clean or repair clogged water filter, blocked or clogged water treatment equipment.


Blocked water piping, clogged water filter or other water treatment equipment A blocked or clogged water filter or pipe or other water treatment equipment close to the water pressure tank can cause very rapid on-off cycling of the water pump, particularly if the filter, valve, or equipment is located between the water pump and the water pressure tank.

Check the order of installation of equipment. Be sure at least one clear water piping pathway is open between the water pump outlet side and the water pressure tank inlet side.

Replace a dirty, clogged, or suspect water filter cartridge.

Watch out: turn off the pump right away to avoid damage.


Plumbing Fixture Problem: poor flow at individual fixtures

If water pressure is good at some fixtures and bad at others, remove the faucet strainer or shower head at the bad-flow fixture. If water pressure is good without the strainer, the strainer was clogged.

Check that the control valves for the fixture are fully open.

Check for a clogged pipe, elbow or valve serving the poor-flowing fixture.

Clean or replace clogged fixture strainers.

Open or replace stuck, partly shut fixture water supply control valves.

Poor hot water flow or quantity

Hot water flow weaker than cold water flow
If cold water pressure is more than hot water pressure and flow then the hot water piping, tankless coil, or water heater may be clogged with minerals.

Clean blocked piping or coil with acid (dangerous and not permanent) or replace clogged piping and equipment.

Check the hardness level of the water supply and if necessary install a water softener.

Well piping problem: Air lock in well piping suction line If the horizontal well piping between well and building does not slope continually upwards or if it has a high spot, an air lock can form in the piping.

Piping may have to be re-run with proper and uniform slope.

Piping or fitting leak on the suction side or well side of the system

A leak in the well supply piping anywhere between the water pick-up point in the well bottom and the entry to the water pressure tank can cause loss of water pressure and water pump short cycling. (It can also cause air entry into the piping system).

For shallow wells install a pressure gauge on the suction side of the system. If your well is a deep well (2-line jet pump) install a pressure gauge on the pump if an attachment point is available.

Let the pump run until it reaches its cut-off pressure. Note the pressure on the gauge. Turn off power to the pump. Turn off water leaving the pressure tank and feeding the building - the valve on the "discharge" side of the system.

Alternatively, after closing the water valve on the output or discharge side of the system (stop feeding water to the building), use a bicycle pump to pump air into the system at the air inlet valve (if your system has one). Pump to 30 psi.

Watch for a pressure drop. If the system won't hold pressure then there is ale a leak on the "suction side" of the water system.

Leaks may be a bad check valve, foot valve, or piping connection anywhere between the pressure tank and well bottom.

First check and tighten all above-ground well piping connections to be sure nothing is leaking. Remember to check or replace any above-ground check valves that may be leaking.

Repeat the test.

If the system still won't hold pressure you will need to pull the well piping and check for a defective or leaky piping connection, check valve, or foot valve.


Bad water pump control switch tubing, clogged or leaky

Clogged or leaky tubing connecting a water pump pressure control switch to the water system results in failure to properly sense and respond to water pressure.

Debris clogging can also occur in the bottom of the pressure control switch where it mounts or connects to the tubing.


Check and clear tubing blockage (blow air through tubing). Or install new tubing.

Be sure tubing is proper diameter and type to seal properly with other fittings.

Tighten tubing fittings to be sure there are no water or air leaks. Soap solution may help find air leaks in tubing fittings.

Clear or replace clogged pressure control switch if the bottom sensor opening is clogged and cannot be cleared.

Pressure regulating wire or valve stuck or incorrectly set (deep wells only) Check the valve setting, inspect the valve for defects Reset, clean, or replace the pressure regulating valve on the deep well pump or piping
Well pump parts worn or defective

Worn or broken pump impeller parts or bearings, or debris clogging inside the impeller assembly will reduce pump output even though the motor appears to run normally. Complete clogging or badly damaged impeller parts or bearings will stop water output completely.

Disassemble the well water pump impeller assembly, inspect for damage, clean or replace suspect or damaged parts.

If necessary, for example if parts are badly rusted and cannot be disassembled and cleaned, replace the entire pump.

Wrong well pump ejector assembly installed in the well

Plugged ejector assembly, tailpiece


If the wrong ejector has been installed in the well, not properly matched to the pump, water flow may be inadequate.

If the ejector is clogged, damaged, or leaky, water flow to the building will be reduced.

To diagnose and correct this problem it is necessary to pull the well piping and inspect the ejector, tailpiece, foot valve or well screen for clogging

Clean or replace the clogged ejector

Clogged foot valve or well screen in the well If a well screen or foot valve screen has become clogged with debris water flow to the building will be reduced.

Clean or replace the clogged foot valve screen, or well screen.




Notes: Some of the well pump troubleshooting suggestions in this list can be found at the Betta-Flo Jet Pump Installation Manualfrom the National Pump Co.

Article Series Contents


Continue reading at TABLE 1: PUMP WON'T RUN, WON'T STOP, or CYCLES or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.


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TABLE 3: PUMP RUNS, NO WATER or INSUFFICIENT WATER at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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