When the thermostate for the morning goes to 68 (from 60), the
furnance kicks on and runs about 1 hour. Then it stops, even though
the thermostate temp is below 68.

It goes into this cycle:

-- big blower fan runs slowly

then..
-- a small blower kicks on for about 25 seconds
-- the ignition element begins to glow for about 15 seconds
-- 3 of the 5 burners ignite for about 5 seconds
-- the elements stops glowing
-- the burners go out
-- the small blower stops after about 15 seconds
repeat the above


When it started up the last two mornings, it did run for an hour
before we went into this start/stop routine.

I'm looking for hints/tips before I call any repair shop.

Regards,