I'm not sure if its a problem with the sensors or the design. I think instead of starting gently the motor starts hard and the intake pressure drops to zero for a split second causing hammer in the intake line. When it thumps it hammers the intake line the hardest.

I attempted to run the pump with no internal check valves and it still thumped. I no longer believe the thump is from a check valve. I realized the intake pressure going up to 40 from 30 when the pump stopped was the pressure of the moving water get trapped on the house side of the system check valve. This time I could hear the inlet check valve close with a very small click. I removed the outlet check valve and reinstalled the inlet check valve. Initially the pump stopped thumping and ran better but it did not last, it began thumping again within the hour. My biggest question is this something that a functioning inlet check will fix or is it likely a design flaw and should I just get a refund and get a different pump. I'm waiting on the RMA to go through to refund/replace, the pump. The intake pressure jumps around quite a bit during this and I think it confuses the pumps controller and it runs erratically trying to maintain a constant output. When there is a call for water the pump starts and the check valve slams open causing the thump. It appears that inlet check valve is allowing enough flow backward to pressurize the line between the pump and the check valve where it comes into the house (about 15' of 3/4 cpvc). I finally got around to trouble shooting it today. When I set the pump any higher than 40psi it thumps when it kicks on and then runs erratically, changing rpms sometimes stopping for a split second, which results in another thump when it starts up. I bought and installed a Scala2 pump to help with my low pressure due to elevation.

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