Dosing. Are you dosing differently? thunking, or not thunking the pf after grinding into it? Or thunking it differently? Started, or stopped using a WDT tool? Different leveling? different tamping? eg if you suddenly become obsessive about tamping, or leveling, that can change things - a lot. I doubt your RR45 is the prob - even if you got a bad bean or rock, I doubt the effect would last more than a dose or 2. it's a beast. Take a long look at whether your dosing procedure has changed - especially if you think those changes would have improved things! At the moment I grind into the basket and thunk it a number of times to settle the grounds, then level it a tad with my finger, poke a tamper at it. I do not precision tamp, precision level, or precision anything. My baskets are just common, ridged, "double". last pull was 1:2 18.5g to just under 40g 25s from first drop, GH Monte Carlos. But I should have not run the pull quite so long - more toward 1:1.5 (edit, yes, that was much better - 15s 30g)(RedBird Mtn High)
hth.

I have recently changed beans. I was buying from a roaster in California and their beans were very dark and oily. They raised their prices to the point that I purchased beans locally. The local market roasts beans for their use as well as for selling them. The beans are not quite as dark and only slightly oily. I have had to set the grinder for a finer grind to maintain the 27-second shot time. I added a Barista Gadgets temperature gauge. Are these gauges any good? The boiler seems to idle at a tenth or two around 100 degrees. I am wondering why the water temperature varies little during the shot. I clear the head for a few seconds before installing the portafilter. The water temperature does not seem to change during the shot time. I use a leveler on the coffee before I tamp. I time the shot from when I turn on the pump. I always had dry pucks before the change in beans. Now the pucks are wet and come out to the basket in pieces.
A little grappa in the coffee really improves its taste.

I've never heard of Barista Gadgets nor can I find it easily on the Internet. That you're only seeing a fraction of a degree of variation seems as though it isn't providing very valuable information. The EricS group-head thermometer for an E61 HX is an excellent choice.

Are you certain you're tasting sour and not bitter?

Dark and oily beans, or even dark and not too oily beans are comparatively hard to get to the sour side and relatively easy to get to be too bitter.

Local beans are also no guarantee that they are good quality, well roasted, well cared for, and aren't stale. That it is a "local market" and not a professional coffee roaster doesn't instill confidence for me. Your espresso will be limited by the quality of the beans.

Not my proudest moment in home roasting, but I did figure out how to make a roast look just like Full City (dark, slightly oily) but with grassy and sour notes - very off-putting for my dark roast preferences. Looks can be deceiving, so I second the motion that beans aren't fungible.

@David6FL - you stated that your boiler is around "100 degrees". Are you certain you meant to write 100 degrees (Fahrenheit)? That's around human body temperature. Double check your temperatures.

I drink medium to medium-dark & brow starting around 198* then adjust temp from there.

Sorry I didn't specify. That 100 degrees C

I bought the Barista Gadgets thermometer on eBay. When I got it I wondered about its response time to temperature change. The probe has a lot of mass. What is an EricS thermometer? It's probably a useless gadget.

Sorry, I meant the Barista Gadgets thermometer was a useless gadget.

Here's one of the early threads Monitoring Brew Temperature - E61 Groups

As EricS' design proved to be very effective and successful, there are copies on the market now. The quality of the copies vary widely, as do the ethics of those selling them. I much prefer the original, for many reasons.

I found this video on YouTube comparing 3 temperature sensors; http://www.youtube.com/watch?v=mbLQyrCAasI The one marked Coffee Superior is identical to my Barista Gadget. I guess these were marketed under various names. The stem is 17mm long with 9mm threads and 7mm of a tip.

The problem I have is that my machine is not plumbed to the water line. With a long cooling flush, I would be refilling the 1.7L reservoir continually