This sounds like a thermal cut out problem due to fluff build up in the system . Check filter and condenser unit and behind the condenser for blockages . You may also need to take off the heater cover panel at the rear and check inside as fluff accumulates there also. the thermal cut out automatically resets when it cools down but will fail if triggered too often . Remember , always isolate machine from the mains before any attempt at repair.
spindoctor
July 2011