Shower Head Pressure Intermittent

[rsmithplumb]

New home that has a Navian NPE 240A2 with external circulation loop and I have noticed over the past month that the water pressure in the shower heads will for a brief second drop and then come right back. There is no temperature change just a slight loss of pressure for a brief second. It starts happing after the shower is on for about a minute and then happens every 15 to 30 seconds until I turn off the shower. I have 3 showers this is happening too. All shower heads are Moen. The drop happens so fast I cannot tell if it is happening at the faucets. In the showers it seems to only happen when the hot water is in use. Any place to start looking for the problem would be helpful.

Thanks

 

[Breplum]

Doesn't ring a bell for me as a tankless WH thing. The pressure from city water is pretty robust and normally provides even flow.
Check for cross connection flow just for hoots: turn off the cold supply at the WH, then open any hot tap, allow to depressurize...then there should be no flow at all out a hot tap...don't try at the shower, just a faucet with hot only.
If there is any continuous flow, that is a problem.

 

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[Reach4]

Your own well? If so, you may have a bit too much air precharge in the pressure tank.