flamerite mariner fire blows cold after about a 2mins?

hi i have a flamerite mariner electric fire . when i first switch it on it blows out warm air . but after about 2mins it starts to blow out cold air and will not blow warm unless i switch it off and leave for about 10mins and switch it back on then it will blow warm for about 2 mins again and run cold air again . any ideas pls

brian reed
August 2011