A P141F is a generic code set in the ECU for a burner malfunction. You need to retrieve the code from the BCU, and a generic handheld scanner in most cases will not communicate with the BCU (burner control unit). There are a series of tests you can run with the DX2 dealer software that would more easily diagnose this issue, the fuel pump is NOT on constantly and would be hard to diagnose without the dealer software. It is in a very unassailable spot to boot. You could give it a dedicated power and ground and make sure it is running but I suspect your issue is elsewhere. I have replaced only 1 fuel pump in the 7 years the fuel pump has been in use.
The Nozzle has a filter in it, you need to remove it and spray brake clean through it, even then it might still be plugged. I have had some you can spray brake clean through, yet when on the truck the nozzle pressure was as high as 20psi. The only way to 100% verify proper nozzle pressure is to command the master air valve on and monitor the nozzle psi. If near 150k replace it.
Have you removed and cleaned the igniters? Remove them both, clean the soot off them and re-install. Note the condition do they look wet, heavily sooted, tips worn? There is a go-no-go gauge that is used to set them to a specific gap. If near 75k 150k replace them.
The flame temp can not be just ohmed you need megometer to induce voltage and check the insulation resistance as well. These meters are roughly $700. If it is bent replace it. If it is near 75k or 150k replace it.
How many miles? If near 75k, or 150k you need to perform the scheduled burner maintenance.
75k replace the flame temp, igniters, burner fuel filter, clean the orifice hole, clean nozzle and check nozzle pressure.
150k remove the DPR and have it cleaned (if soot on the outlet replaced), replace igniters,nozzle, flame temp, burner filter, clean orifice.
If there is soot in the tailpipe or on the fuel tank the DPR is most likely breached and needs to be replaced. (remove and inspect, if soot on outlet replace and clean t-pipe)
Hino after-treatment warranty is 5yr-100kmi. unless you have extended coverage, but most do not. If you are within the 5yr 100k mi, It may be a warrantable failure. If you pm me your vin I can check for recalls and warranty coverage.
Usually when re-gens take a long time to complete there is a temperature issue, there are alot of things that can cause this. A little more info would be helpful. Thanks