We have a similar Kohler steam generator and have no such noise issue. It doesn't make sense that after several hours, certainly 24, that the steam generator would be the source of a temperature related expansion/contraction noise.

Regarding a PRV, that is a Pressure Reducing Valve used to take (varying) incoming water pressure and reduce it to a constant output pressure to supply the house. It is usually installed in the water supply line soon after it enters the home. With a PRV, a small expansion tank needs to be placed downstream of it (usually in the hot water line after the water heater) because the PRV also acts as a check valve and cold water expanding due to heating in the water heater can create substantially high pressures which would cause the water heater temp/pressure safety valve to open and discharge water into the home.

I have a PRV where it enters the house. Kohler sent me a new unit but I am not confident it is a unit problem. I don't really want to send the $$ to have someone install the new generator just to have the same problem, but so far my problem seems to be pretty unique so maybe it is a defective generator.

Mine is doing same thing. Found this cause I GTS ( googled that sh#t)

I also have the same issue.

Before you blame the unit, it is very likely that it's due to air in your pipes or excessive water-pressure or both. You can google how to remove air from your pipes at home, if that doesn't work, get a reliable plumber that is familiar with dealing with water hammer. You may want an expansion tank near the steam shower unit.

I have the same issue can any one link to a solution

Same issue. Called Kohler and they told me it’s normal. Shame on them. This is a maddening noise. In owned a Kohler unit prior to this which never made this noise.

I have the same problem I put on a pressure regulator still making the same nice

Make sure there is a drop to the pipe from the shower to the generator and the generator is perfectly level in all directions.

I have the same issue. I have had a steam generator for 10 years, no knocking sounds. I had to replace my unit as it failed, I ordered direct from kohler. the unit lined up exactly to all previous connections, so a direct swap out. super easy. Then the knocking began. It is driving us nuts! i called kohler, they said run PCM, bleed system, empty unit and refill. Nothing has worked. my only solve is to shut off the circuit breaker to the steam generator when not in use (not ideal as it is in basement 2 floors below). IMO, it seems related to the float inside not ever closing to connection, or somehow the water is causing the float not to sit properly and it never shuts off. whatever it is, i would love some input as i loved my steam generator, now it is a constant banging noise during the night. is there a solution in sight?

Kohler has an issue in the design of this unit. They will not admit it though. I have had a Kohler warranty tech at my home multiple times. They replaced all the parts inside the unit and it still turns on and off while using the steamer. In addition it keeps making the knocking noise when idle. Kohler has sent me two new timer controls as well but it continues to have issues. This is the second Kohler steamer I have owned and probably my last.

Same issue. Last home the unit was silient. This home the new unit sits in basement dieectly below the shower and sound is evident upstairs in the bathroom with steam shower. Most noticeable at the steam output in the shower. Only hear it in the evening and does not appear to be related to ise of the steam sauna.

unit is level and all pipes drain back down to the unit.

sounds like a kettle boiling… Will troubleshoot by shutting off the breaker to see if it is electrical or mechanical.

Same issue my unit is about 2 years old and I have a loud knocking noise says after I use it.

FINALLY A SOLUTION TO THAT BANGING SOUND!!!!!!!!!

Had to use caps as I am damn proud to share a solution to this constant banging sound from my steam unit. Over a year of continual banging and it is all over....

The fix is super easy and takes only about 2 minutes to complete.

The banging issue stems from the sub heater that keeps the unit always ready to make steam at a moments notice. If you disable the 'instant on' feature the banging stops entirely. The only downside, which to me is not a downside considering the banging is gone, is that by disabling the sub heater the unit will take 3 to 5 minutes to generate steam. I can wait a couple of minutes to have steam vs banging all day and night. Be sure to wrap tape over the connector to ensure it does not come in contact with any other objects which could create a short.

I took a picture and added the steps to the image. The steps are also below in text:

Steps to stop that knocking noise:

1 - Turn off circuit breaker

2 - On back of unit, remove 4 screws

3 - Remove control cable (Phone like cable)

4 - Pull control panel/back panel out, wiggle it out

5 - Locate white wire labeled “SUB HEATER” (circled in image)

6 - Use pliers to pull connector out of control panel

7 - Use electrical tape and tape over blue connector on end of wire

to avoid it coming in contact with anything else inside unit

8 - Tuck wire inside unit

9 - Push control panel back in place, insert 4 screws and tighten

10 - Plug back in control wire (phone like cable)

11- Turn back on circuit breaker

12 - Never hear that banging sound again. Cheers to quiet.

(this disables instant on steam - will take 3 to 5 minutes for steam)

This works 100% to stop the noise.