btw I replaced the dpf filter two years ago and about 300 hours ago
When this was done was an ash model reset performed using Cat ET? It's a must.
Also why was the DPF replaced? Was this done as preventative? Or were you getting codes or events?
Also are you still seeing the E1239-3 event active?
Any other codes/events active?
back to my original question: is there a list of conditions that have to be met?
No. As I said earlier on this could be something as simple as a sensor input to the engine ECM reading slightly off skew. Inputs include fuel pressure, mas air flow (boost), DPF temp sensors, DPF pressure differential sensor, coolant temp, etc, etc, with fuel pressure, DPF press differential and boost pressure sensors being the most common to give you trouble. Fuel temp is just one of those inputs so there's no doubt in my mind you've done the right thing by correcting that active code.
A good example is the DPF differential pressure sensor. If it reads just half a psi off skew this effects the soot loading model in the ECM roughly 25%.
It's a simple check to do with ET, but it obviously means you need to call someone out. If you do, demand they provide you with a copy of the Product Status Report pdf file and post it up here. I'd need to see DPF #1 Soot Mass readings.
With key on engine off, are there any sensor parameters you can see in your display?