New valve cover = bad thermostat?

[Treats54]

Just replaced valve cover on 2013 x5 35i. No leftover parts! However, since then I do not have heat inside and I am getting CEL p0128 for a bad thermostat. Not sure how I would have fouled a thermostat. Wondering if I knocked something else out of whack. Any suggestions before I take it to a BMW shop?

[X5Sport]

The 35i isn’t a model in the UK so I’m assuming that you’re in the US (or at least not in the UK). Did you need to disconnect any plugs and forgot one once it was all back together? You wouldn’t be the first (or last) to have made that ooops!. Could be a bad ECT (Engine Coolant Temperature) sensor - it’s somewhere below the intake manifold, bad stat, or just bad luck that the issue occurred at the same time.

[Treats54]

In US. I thought I might have knocked a vacuum line somewhere. Went back and took it half apart gain to make sure everything was connected. Did not find anything off. Did a smoke test and did not see any leaks.

[Alan Gunn]

My money is on a plug off or in the wrong place.
As X5Soprt said you won't be the first or last.

[Treats54]

When driving, I can hear either a fan or a blower that sounds like is is workig overtime