Since I am not able to send this issue via the "ask a question" form on the website to the Fairphone support theme, I will post it here hoping somebody can help. On forehand I would like to mention that I think this issue is not discussed before despite that the symptoms are comparable to other issues.
My daughters Fairphone 2 keeps rebooting. We read through your FAQ and forum and decided to do a factory reset. Unfortunately immediately after the factory reset, just around the point where the android installer asks for the gmail account, the phone keeps rebooting in a cycle. During this cycle the reboot cycle time decreases dramatically to the point where only the Fairphone startup screen (the black screen with white Fairphone text) that appears immediately after starting the phone, is visible for a few seconds whereafter the phone reboots and cycles in this loop. If we put the phone away in a cold place and wait for it to cool down we can finish the factory reset but whenever we start using the phone, e.g. install updates from Google's Play store the reboot issue starts again.
What we tried so far:
-> factory reset
-> remove SIM and SD card; didn't affect the problem
-> changed the screen with the screen of my FP2; didn't affect the problem
-> changed the battery with the battery of my FP2; didn't affect the problem
-> reinstalled the latest firmware via the Fairphone updater; didn't affect the problem
Regarding this problem we have noted the following:
-> the reboot cycle time is correlated with the "temperature" which can be felt at the back of the phone at the position with the text "yours to open // yours to keep". The hotter this spot gets the faster the phone reboots
-> if we put the phone in a cold place it can be used for a longer period
-> After the factory reset we installed WhatsApp, Telegram, Signal and CPU-Z. We checked the temperature of the phone via the tab "thermal" in CPU-Z. Compared to my Fairphone at approximately the same temperatures 50-60 degrees Celcius on both phones the spot "yours to open // yours to keep" gets much warmer on my daughters phone.
-> just before the phone reboots everything freezes for a second or two.
Furthermore I would like to mention explicitly that I think this case is different from the cases "my fairphone gets hot" and "my fairphone reboots randomly" in the FAQ and on the forum since those cases seem to be caused by installed apps or a high processor load whereas this case occurs:
-> during the factory reset process with no apps installed other than those during integrated in the android installer
-> when the spot "yours to open // yours to keep" gets hotter than another Fairphone with comparable internal temperatures (derived from CPU-Z)
I hope someone can help us further to get this Fairphone back to normal operation.