Condensation inside low-E double pane windows?

I have Milgard windows in my house, vinyl-clad, double pane. I forget if they’re filled with some kind of special gas. Anyway, I noticed condensation all around the edges of the inner pane of the bathroom window (there had just been a bath in there) and I don’t understand it. Is this indicative of a faulty window that needs replacing, because it’s nowhere near freezing out there, it’s 43F as I write this. I’ve never noticed it before, except on aluminum-frame windows (we had a terrible time with those, and had them replaced.)

Your window has a leak, and it has sucked in some moist air during the normal daily expansion and contraction. It’s probably not a big problem, but the window is not as good an insulator as before.

Contact Milgard, or their local dealer. There’s a good chance they’ll replace it for free. They don’t want their windows out there looking bad. If it comes down to you paying for it, it’s a personal decision based on appearance.

I bought Milgard Windows because of their Lifetime Guarantee

The glass is usually SEALED to prevent leakage of gas out or water vapor in.
If the condensation is on the house side of the inside glass it is due to condensation.
If the condensation is between the two glass panes call Milard tomorrow!

I work at a window manufacturer (not Milgard), and this is the number one service issue. Typically the glass unit is sealed in a manufacturing plant that has a - less than clinical environment - so dust and other particulate matter (glass fragments, vinyl dust, saw dust, etc) can find its way between the spacer and the glass. This will allow air (along with moisture) to leak in, and the (typically) argon gas to leak out.
If you don’t have this serviced, you can watch the LowE coating (which is actually metallic) slowly rust in interesting patterns.

Rereading the OP, though, it sounds as if you’re talking about the moisture being actually inside the house, rather than inside of the sealed unit. If this is the case, then no, there really isn’t a fault with the window per se.
Most (if not all) manufacturers will not warranty condensation issues.
If these are new windows (or at least if this is the first winter with these windows installed), you could just have a better air seal than the old windows, which could actually cause the moisture to collect on the glass more than it would have otherwise (think of a room with a window that is wide open, the air in the room will more closely match the temperature in the surface of the glass, and condensation will be less likely to occur).
There’s a lot of moisture in a bathroom, and it will condensate on surfaces that are colder than the air in the room (cold pipes, glass in a window, etc).

When I was a kid, my dad fixed one of these windows by very carefully heating the seal with a propane torch and melting the seal on the outer pane of glass and taking the glass off. He dried the inside off and then reattached the glass sealing it with Liquid Nails. It held for five or so years before we sold the house.

Of course, this is the poor man’s way of fixing a leaking double pane window that never had a warranty.

If you are noticing water condensation on the INSIDE of the glass, it is leaking somewhere, like everyone else on the board has pretty much said.

I watched someone on TV use food coloring to figure out what side is leaking. He would trace along the seam with blue food coloring in an eye dropper and let it dry. If any ended up on the inside, that was the side leaking. I don’t know how well this works here in the real world, I have never tried it.

Good luck.