Hi Liz, while phones can overheat I've never encountered a single app getting the blame. Can you confirm that the message specifically mentioned CT?

Also, is 'I was not able to turn it back on for at least 20 minutes.' referring to the app or the phone?

If it is indeed the phone it would be helpful to share make/model/age. Did you have any other apps running at the same time? Where was the phone? Is it in a case? 

In relation to CT, were you making use of energy saving features such as 'dim between turns'?

In my experience, exposure to direct sunlight can cause a phone to overheat - especially the cheaper models I tend to favour. I find too, that phones that are full (or nearly full) are less efficient - and prone to heating up. It may be worth referring to the literature about your specific phone or doing a quick Google. 

However, you do raise a relevant issue in depending on a phone for navigation. Used on the handlebars it is exposed to nature and potential accidents. When something goes wrong we may not be able to use our phones. For this reason, it may be worthwhile considering using a second phone for navigation. It can have advantages as a backup for all our important apps - not just navigation. 

That’s a curious one and not something I’ve encountered before! Am I guessing this is Android? (What phone model do you have?)

Two outside possibilities that might help: try switching to another map style (in particular, the app has to do quite a lot of thinking to show Ordnance Survey maps), and turn off ‘Automatic route feedback’ from the settings menu. 

Yes it is Android - Samsung Galaxy A20e which is a few years old.  The message definitely did say specifically, "Cycle Travel closed as it is overheating your phone".  I was not able to turn the app back on for about 20 minutes, although the phone itself stayed on.  It was mounted in a holder on the handlebars of the bike and it was a sunny day, but being March, surely not that hot.  We did stop at a cafe en route and maybe I should have removed the phone from the holder instead of leaving it out in the sun while there.  The map style was the standard one used on CT and I had no other apps running.  The phone battery ran out before I completed the route, so I have now changed the settings to "dim between turns" which hopefully will help, and I will carry a portable charging stick and lead with me.  Also a paper map!