Blinking cyan after several hours of connectivity. Reset corrects issue...temporarily


I have a Photon that is several years old. I recently deployed it on a newer wifi network where it seems to run flawlessly for several hours…before it loses wifi connectivity and begins blinking cyan. Hitting the reset button always seems to correct the issue - it blinks green and then re-connects to the wifi and breathes cyan. Several hours later - the problem reoccurs.

I have searched the forums but wasn’t able to locate a post that dealt with the specific problem I was having (there were several posts that discussed DFU mode, and occasional red bursts, but that’s not what I am seeing).

The problem unit has firmware 0.8.0 rc10. I have other photons working great with firmware 0.7.0 rc2.

Any thoughts? Thanks.

Long Term Photon Connection Stability

Are you using lots of String objects?


Thanks for the response.
I actually only have 2 string objects in total. Also, I have the identical application running on other photons and they dont exhibit the same behaviour.


@bjagpal It would be worth your while downloading the diagnostic report from the console if you are running 0.8.0-RC.10. You should be able to see what the cause of the network connection is and if it is memory leakage/low memory. I did this recently with about 11 devices (Photons) running 0.8.0-RC.10 that had been highly problematic. The issue actually turned out to be related to loop cadence. Essentially there were 2 problems: 1. a read operation from SD card would occasionally cause the loop to go very slow - this then backs up the connection stay-alive process - what Particle.process() does or normally happens each loop [I will get corrected here by someone with more knowledge]. 2. A number of capacitive touch buttons connected to pins with interrupts were firing off when they shouldn’t have - again reducing the loop cadence. Solving the cadence issues has sorted the connectivity problems. However, if you don’t have interrupts and you don’t read from and SPI SD card then they can’t be the causes of what you are seeing!


Hi there, thanks for the response. The application code that I’m running is very simple - it doesn’t use interrupts, nor does it read from any external storage. I don’t think there is anything wrong with the application code since it is running fine on a couple of other photons. The only difference I can see is that the firmware is slightly newer on the one that’s giving me problems.

Right now I’m thinking of two potential causes:

  1. the firmware is causing an issue, in which case I may need to revert back to a version that I know works with my code (ie. 0.7.0 rc2.)

  2. this photon in particular has given my problems before; after a lot of troubleshooting, I deemed it to be hardware related. Specifically, it seemed to be draining batteries at a much higher rate than other photons in the same set up. It could have been related to it not going to ‘sleep’ when it should have.

Anyways, what I was ultimately after was an explanation of the blinking cyan light. I was hoping someone else had seen the same issue. Again - it loses connectivity, blinks cyan, and only re-connects on a reset.


I would try to look at the DHCP logs in the router that the Photon is connecting to. You should also check the DHCP lease time to see if consecutive occurrences of the blinking cyan correspond to that lease time.

It would also be good to write some test firmware to check RSSI etc.

An easy way to tell if your code is causing the problem is to load up Tinker and run it overnight instead of your firmware. If Tinker fails too, then you can assume it is not your code. But if Tinker runs without issue, then you have to look at your code.


The photon has stayed on for: 9 hrs, 13 hrs, 17 hrs, 16 hrs. I was hoping to find a pattern but was unable to do so. Looking into the DHCP logs sounds like a good idea though…

The tinker suggestion is also a good one - I think I’ll try that one out sooner rather than later.

PS - still wondering what the blinking cyan actually means.


Blinking cyan means it cannot connect to the cloud. There are many possible reasons include a dual mode router (2.4 & 5 GHz) that tries to push devices to 5 GHz, key issues, CoAP port issues, etc.

Another good thing to make sure of is that if this is a dual-band 2.4 and 5 GHz router, the two bands should have different SSIDs so that it cannot try to move your Photon to unsupported band.


Ahhh great, thanks. I will look into that link…


Does it make sense that resetting the device allows it to reconnect to the wifi and stay online for several hours?


Yes, particularly if the router is to blame. If you can rename the SSID for the 5GHz band on the router, that is a quick fix.

If you are not getting orange/red flashes with blinking cyan, then your keys are OK (and you can get online normally after a reset). Since you reach the cloud after a reset, you not likely to be having a blocked CoAP port or similar issues.


Excellent. Thanks for all the help. I was going to reset they key but I will hold off on that. I will look into the router. Now that I think of it, this unit was working fine when I had it connected to a different router.


Just wanted to provide an UPDATE: after running several test scenario’s I have come to the conclusion that the issue I was having was related to the system firmware that I had installed on my photons. I was using 0.8.0-RC.10 and the units would invariably go into the “flashing cyan” mode after several hours; it would only reconnect to the cloud after I reset my photon.

Earlier this week I “downgraded” the firmware to version 0.7.0 and my photons have been working fine ever since. It’s been 5 days and counting. My photons do lose connection from time to time, but they always recover on their own.