It is a well known fact that tankless causes pressure drop the higher you flow water through it. We have two Rinnai 75Lsi heaters, originally plumbed together in a manifold, then with a manifold with a pressure activated valve.
1. With pressure valve low flow faucets cut water heater on, but get loud water hammer from Kohler shower mixing valve during high flow. Called Kohler and they said any difference between hot and cold greater than 5 psi will cause hammer.
2. Took pressure valve out, no water hammer but low flow faucets can't trigger heater. Each single unit requires 0.4 gpm working together using EZ connect this must be 0.8 gpm?