Cycling too fast?? Furnace or thermostat

Hi,
My furnace is about 6 months old and we started using it just last month. I replaced my analog thermostat with a digital one (Honeywell CT3200). I've programmed it to go down to 17C when I'm not home and after 6PM to go back to 24C. However, when we got home last night at 10PM it was 17C. I tried clicking 'Run Program' and the furnace made a clicking sound (3 clicks) but no hot air just a humming sound and that even stopped. Then I clicked on 'Warmer' button and raised the temperature setting to 24C. It ran for 10-15 seconds and then it stopped. Clicked on 'Run Program' again and same thing. All you hear is the clicking sound. The furnace makes a humming sound but no air. So as the last option I clicked on 'Warmer' button and raised the setting 24C and clicked 'Hold Temp' and then the furnace began working fine. This morning I woke up and it was on 24C as set. So raising the temperature to 24 failed, clicking on Run Program failed but raising the temperature and clicking hold works. Anyone knows what could be causing this? Is it the thermostat or the furnace? Also, the blinking lights in the furnace indicate that it's running normal.
Also, there is this setting in my thermostat that says 'High-efficiency furnace such as a 90% or greater AFUE (unit) must use this setting and under 90% must use this setting. Could this be causing it?
Your help is greatly appreciated.
Thanks Maz.
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snipped-for-privacy@gmail.com wrote:

Motor's stuck.
That it ran later proves whatever was binding it broke loose. Might still be floating around in there. Hear any rattling?
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