Pella is pretty low quality. That and purchasing them from a big box store you probably wont get much service from them. Maybe someone on here has a nifty fix. I'd think replacement but I know some people are fans of storm windows on here. They can some times make windows perform a little better, I don't have much experience with them though being on the west coast.

Pella is an exceptional marketing company masquerading as a high end window manufacturer.

How did they fix the issue the first time?

Not much you can do to that to fix it on a window basis if the windows were checked previously for proper fitment.

Time to look at interior storms.

I'm afraid that I'd have to agree with the other pros. If the installation is correct, there is probably not much that can be done. The fact is that it just is not a very tight window product. I had a project with Pella Prolines some years ago where there was actually air leakage between the sash and frame causing frost--- and these were fixed picture windows! That and the customer service that I subsequently received helped shape my view of that company and product.

Notorious leakers. Good luck with that.

Why does Pella refuse to take "any responsibility"? Were the windows installed and shimmed correctly? Pella uses a pretty narrow frame compared to others which if not shimmed just right will flex/bow out over time and you will have gaps between sash and frame. Taller units are more prone to this. There is a pretty strong spring balance with a block and tackle inside the jamb that is exerting force on the frame. When you buy the windows you will see a nylon strap at the check rail that you cut AFTER you have installed and shim the windows. That strap keeps the frame from bowing out at the middle. I bought a brownstone where the builder had gone bust during construction. It had Pella Architect DH windows. The unit had already been bricked, but none of the windows were shimmed. It had sit for 6 months and you could see light around every sash. We cut the brick back and spent around $12,000 just fixing the windows and doors, but once they were installed right they worked great.

If the windows are shimmed correctly, then Pella had better get their butts back out there, because they have a product failure. For a tilt-in DH the weather stripping is the only thing keeping air out and closing the gap. If you see a gap then the weather stripping has failed. That weather stripping should have a 10 year warranty.

One thing to point out is that you bought the windows through Lowe's. Here is where it gets dicey with Pella. Pella has distributors who are also responsible for service of all Pella products and they compete directly with Lowe's. At one point in time, if the product was purchased through Lowe's, you had to call a special number to get service from the branch. Lowe's has to pay the branch/distributor for the service work, and if the call doesn't go through the Lowe's call center, then the branch can't get paid for doing the service work. I'm not sure if this is still the case, but at one point many of the local branches pretty much ignored product sold by Lowe's, because they couldn't get paid to service it unless the request came from the Lowe's call center. Things maybe different today, but Lowe's still depends on one of its competitors to service what it sells, and that often causes problems.

If you are a Lowe's customer who is waiting for the Pella branch to come fix you windows, realize you are at the bottom of their list. They take care of their customers first.

This is actually not a lot different that other manufactures. Most manufacturers contract out with a company to do their service work in an area. One company might perform the service work for 3 or more manufacturers. The manufacturer who pays the most gets the best service from the 3rd party service provider, and their customers take priority. Manufacturers who don't pay well, don't get good service coverage. Of course some manufacturers have no service at all. Their warranty is simply for parts and they will send you the parts and you have to fix it. It is your responsibility to show that the part is defective, and there is nobody you can call to come look at it.

In my market Marvin and Pella have the best service of any of the manufacturers, and I dread having to deal with the service departments of either. They are both train wrecks.

I think the last sentence summed it up. Even the good ones are nightmarish to deal with.