This is an intermittent problem, but it is becoming more frequent and annoying, and I would welcome any advice.

I have a 2009 (59) Ford Fiesta Titanium, and in recent months I have had problems with the heater / air conditioning (Climate Control) unit. Without warning, the LED screen which displays the desired temperature switches itself off, and hot air blasts out at full capacity! I can't turn it off, but I can reset it by pressing a button on the left, and this sometimes cures it (it resets to 22 degrees), but sometimes the problem immediately reoccurs- sometimes on several occasions which is an absolute pest whilst driving (have one finger constantly on this button otherwise I roast!) For the first time today, it blew out warm air when the climate control was set to 16 degrees. On the (lengthy) return journey, not a single problem- the climate control / air conditioning unit was working perfectly.
Any ideas what might be the root of the problem, anyone?
Thank you.