jjamesee wrote:I backflush with detergent every 1-2 weeks and but normally I do not backflush with a blind filter, just a regular flush after each shot.

As habit I flush everything with a blind filter (now with the rubber stopper its easy) if I know the machine wont be used until the next day, but thats my habit, many dont do that. The use of the blind filter is to flush all the discharge path even if its without detergent.

You said your machine is fairly new, I wonder if what you taste could be a lube excess that hasnt washed out yet.

Maybe others will chime in on how much worth would be start taking things apart (also depends on how comfortable are you in doing that)

Sure sounds like a temperature issue.. I"m not sure you stated your warm up time.. Is it at least 45 minutes?

My guess is that the group is cold and maybe you are pulling after 15-20 minute warm up. (PID display has nothing to do about your machine being thermally stable) So you pre-flush a bit, but not enough to bring group fully up to temp. First shot colder... but then you are running even more water through group.. so now hot.. by time you clean and prep successive shots up to temp.

I think if it were a contamination issue, you would taste it in more than just the first one every day.

Access to a SCACE? Try your exact same workflow and monitor temps in shots 1 and 2.

Just a guess..