Noritz N-0751M Tankless Water Heater Vibration Problem
The problem turned out to be the manifold pressure. We did not correctly check it the first time (before the video was made). You have to set the minimum and maximum settings using the buttons inside the unit. You do not simply check the pressure. You must use the manifold buttons.
(Instructions to adjust manifold pressure):
On the outside cover (of the Noritz N-0751M) you will see the manifold pressure settings should be 0.65WC MIN and 2.55WC MAX. From what Noritz told me, these settings are with the cover on. Since it is not possible to adjust it with the cover on, they have to give you the “cover off” settings. I think these were 0.91WC MIN and 2.76WC MAX. I believe my unit was initially set to these settings which the MIN turned out to be too high and caused the vibration. I ended up setting the MIN to 0.73 MC. Anything much higher, it started to vibrate and anything lower I got a howling noise.
Remove cover. Remove tap screw on the left side of the manifold and slide your manometer tube on. Make sure your manometer is zeroed out and set to WC before placing the tube onto the unit. There are 4 buttons on the right side (inside) the unit. They are “UP”, “DOWN”, “Manifold Min” and “Manifold Max”. I like to start with the MIN setting first. Turn water on enough to simulate minimum pressure flow. You will see your manometer rise. After it is running for a few seconds, press and hold the “Manifold MIN” button in. This will kick the unit into MIN manifold pressure simulation. You will then see what your MIN pressure setting is actually set to. If you need to adjust the setting, continue to hold the MIN button in and press either the UP or DOWN button to adjust (while holding in the MIN button). When you reach the setting you want, just hold it there for a second or two to make sure it doesn’t change and leave go of the button. Do the same thing with the “Manifold Max” button BUT VERY IMPORTANT WHEN PRESSING THE MAX BUTTON … The unit will kick the manifold into MAX pressure simulation so it must have a lot of water flowing through the unit. If it doesn’t, it will heat the little bit of water that is going through the unit sooooo hot it will turn it to steam and will stop flowing. So, make sure your water valve is opened pretty good before pressing the MAX button. I set my MAX setting to about 2.65WC. I’m not sure if it makes much of a difference going lower, but I just figured my MIN was set a little lower, so I did the same for the MAX.