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Water pump making loud nouse. where to start diagnosis


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We are suddenly getting a hammering noise from our water pump.

1 it has an accumulater tank

2 this is new problem Its always been very quiet up to now

3 plenty of water pressure

4 happens on both hot and cold

5 no leaks found and the pump is NOT trying to run when faucets are turned off

Any ideas welcome

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Is it starting immediately on any draw?

Is it hammering as it charges the accumulator?

The former symptom points to a ruptured bladder, the latter, a loose pump, one of its connector pipes/hoses making hard contact, or something has come into contact with the pump or its connections.

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It could be waterlogged. Following is my procedure for getting it back in operation if the bladder is still good ...worked on mine.

Just to double check the procedure, be sure when you checked the pressure and added the air, you shut off the water pump and opened a faucet. If the air did leak out through the shrader valve and the tank filled with water, you'll find that it will take very little air. Since water is non-compressable, a small shot of air will pressureize the tank if the faucets are closed. Since such a tiny bit of air can be added, it will usually just escape again when the pressure is checked again.
By trying to add air with the faucets open and water pump and city water disconnected, the air will push the water out of the tank and empty the internal bladder inside the accumulator if it is still intact. Once the tank is empty, you now pressurize the tank to 20 PSI as a pre-charge on the tank. After precharging the tank, when you turn the pump back on, it will pump water into the tank compressing the air until the tank pressure reaches the cut of limit of the pump. Once pressurized, you can then check/adjust the pressure. Set to 20psi.
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Any ideas on what the pressure of the tank should be?

If you let it run until the pump stops the pressure will be whatever the pump is set to stop at. To adjust the accumulator you need to turn off the pump and any water supply, then open a faucet to let the accumulator drain and then set the empty pressure. The one that I put in holds about a quart of water and the instructions said to inflate it to 20# with no water in it. According to that it will then be about 3/4 full when the pump turns off and should never go completely empty if the pump is on and working properly. Most pumps come set to stop at 45# and then to start when pressure in the system drops to somewhere around 30 - 35#.


Another possible cause would be if your water line from the pump has moved to where it is vibrating against something solid or if the pump has vibration dampening pump mounts and one or more of those have collapsed or failed in some way. The noise is usually caused by normal vibrations from the pump.

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Hey Kirk. Haven't tried any fix yet. We are suddenly dealing with some unforseen medical stuff. However it quieted down and after filling with water yesterday it stopped. So maybe air in the line??? Will check pressure this week

Thanks for all the help

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At various times in every RV we have owned we have gotten air in the water lines. Air in the lines cause a loud hammering sound. Generally air has gotten in the line when the water tank gets low. Turning on each faucet on at a time for 10-45 seconds clears the line and the hammering stops.


We have never had an RV with an accumulator, so don't know if the accumulator will prevent the hammering with air in the water line or not.

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had the same problem and found a cold water line under the kitchen sink that had moved slightly and was in contact with the cabined wall. I moved it slightly and placed some foam around the hose in the area. could not hear the pump come on at all after that except for 3:00 AM potty breaks.

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