Webasto timer goes off intermittently !!

[Karl]

I have a basic three times a day Webasto timer. The one you can set to come on but not go off ! I cut the black wire coming out the back of it two years ago so I can leave the boat and the Webasto will go off after an hour or also after has been set to come on, go off after an hour. Probably nothing to do with it but last few days sometimes it comes on for 20 mins or even 40 mins or sometimes the full hour wether it has come on with the timer or been switched on manually. Once it goes off I can switch it on again without any problems and the same thing happens. No signs of trapped air as all radiators hot and no noises of air trapped on start up. Also on mains hookup so don’t think it is a battery problem. Can’t figure this one out ?? Never had this problem before !

[matty40s]

Does it have a frost setting temperature??

[Karl]

not as far as i am aware