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Thread: Well pump shuts off prior to pressure switch cutoff

  1. #1
    DIY Junior Member ABrown's Avatar
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    Default Well pump shuts off prior to pressure switch cutoff

    I have been reading through the forum here to find a similar problem but could not find an exact match so I thought I would ask a question.
    I have a 380' well with a 1.5HP 10gpm pump that pumps uphill to my house. There is a bladder pressure tank with a 40/60 switch. The tank has 10 gallons of drawdown.
    I recently bought the house so I am new to well operations.
    Twice now the pressure in the system has dropped to zero and all water stops flowing. The first time I reset the breakers (which were not tripped) and the pump seemed to reset and refill the pressure tank to supply water. It happened again last night while I was taking a shower. We were using the water to wash clothes and dishes prior to both of us taking a shower. When the water shut off on my I once again went back to the breakers and reset (again they had not tripped) but the system would not stay running. I went to the well head and could hear the pump turn on but it would not stay running unless I opened the spigot at the well. I shut the breaker off and opened the well spigot and water would flow so I turned the breaker back on and heard the pump engage and increase the pressure coming out of the spigot. I went back to the house and looked at the pressure tank. Pressure was back to 40psi and the pump was not running but the pressure switch was activated sending current to the pump. I opened a hose bib and the pressure dropped to 0 and would come back to 40 when I closed the bib. Water would flow in the house also but the pressure would not climb above 40. So I went inside and started researching the cause. I really don't know what is going on though. This morning I went down to check the pressure and it was at 40 still. I checked the power at the switch and it was still sending current to the pump. I reset the breaker and the pump fired up and charged the tank to 60. I opened some faucets and drew the system down to 35 but the pump did not turn on. I reset the breaker and the pump turned on again and brought pressure back to 60. I drew down again and the pump turned on at 40 and off at 60.
    Any ideas of what would be causing the intermittent pump/switch/bladder issues? I have not checked the pressure in the bladder yet. I will do that tonight once I get home.

  2. #2
    In the Trades Texas Wellman's Avatar
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    Sounds like the internal overloads in the pump are tripping.

    Time for an amp reading....my guess is that it's pulling high amps.

  3. #3
    Test, Don't Guess! cacher_chick's Avatar
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    If it turns off while running the overload in the motor is probably tripping, but if the motor does not start I would be looking at the control box.

  4. #4
    DIY Junior Member ABrown's Avatar
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    So tonight I came home and did some more testing. The air pressure in the pressure tank is at 36psi and the pump is running at 16 to 18 amps (240v system each wire is at 8 to 9 A so i assume that combines to 16 to 18). I shut off water to the house and connected a hose to the drain by the pressure tank. I turned on the hose and the, the pressure tank pushed water until the pressure dropped to 40 psi. The pump turned on and it sounded like the tank kept draining. Once the tank was empty (this is an assumption) the pressure gauge dropped to 10 psi and stayed there until I shut the valve. With the valve closed the pressure rapidly increased to 40 then slowly up to 60 as the tank filled. I let the system run for about 2 minutes full open but the pump never shut off while the switch was closed and the amp readings never changed.

  5. #5
    Moderator valveman's Avatar
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    A 1.5 HP pump should be pulling around 11.5 amps per leg. And since you checked “both wires” I assume it is as two wire motor with no control box. What usually happens is that after a few years of cycling on and off, heat causes the stator with the windings to swell and start grabbing the rotor. So after the pump has sat idle for a while and cooled down, it will come on and work as it should. But when washing cloths or taking showers, the pump cycles on and off a few times, the windings heat up, swell and start grabbing the rotor. This causes high amps and trips the overload in the motor. After everything is off for a while and cools down, the overload resets itself, the windings cool and contract, and the pump will work again.

    The motor is on its last leg. It is just waiting for the most inopportune time to lie down on you. With a house full of in-laws over for a holiday, or maybe just on a Friday night after everyone is closed, it will decide it never wants to start again. I would get prepared to replace the pump/motor. Then figure out how to stop a pump from cycling on and off so much and it will last much longer the next time.

  6. #6
    General Engineering Contractor ballvalve's Avatar
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    Seems like rotor-stator touching should raise the amp draw. But it may be a 3 wire pump and he's testing the infeed. I have a cap run 1.5 motor that draws 9.5 to 10.5 amps, and its pretty new.

    As to the overheat switch in the pump, why is he sometimes getting the pump to start by resetting the breaker? I don't believe that resets the pump internal switch. Perhaps he should start with the control box if he has one.

    Or maybe he has a cycle stop valve and thus has reduced amp draw....

  7. #7
    DIYer, not in the trades LLigetfa's Avatar
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    On a 2 wire 240V, both legs should read the same current and no, they should not be added together for a total. If one leg reads different, there could be a bad heatshrink, bare wire, or other leak to ground.

    Toggling the breaker could be putting the motor back onto the start windings for a kick start.

  8. #8
    DIY Junior Member ABrown's Avatar
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    I took the readings from the feed wires coming off the main breaker panel which then go to the pressure switch and off to the well. I will go check the control box down by the well head tonight. I don't know if this will help but, according to the well log, the pump was put in service in 2005 and is a Grundfos 1.5HP submersible.

  9. #9
    Moderator valveman's Avatar
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    Now that we know it has a control box, it is probably a start cap, start relay, or both. Check out the control box or replace it before you do anything to the pump. A bad start cap or relay is one of the first signs of cycling. If it hasn't already happened, next will come what I described above.

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