I have a Hoover HSWD 126 and after about 11 months old, the heat stopped working in the tumble drier. The cause was the condensor which gets full of fluff. Because the sensor senses this blockage, the safety thermostat cuts out. You can reset the thermostat, but you will probably keep getting it cut-out again (no heat). Ideally the condensor needs emptying or possibly replacing. Mine has now gone again after being cleaned in March, so I am either going to look for a new vented drier only, or just look for a condensor to fit my Hoover.
For me, the three or four bolts at the rear, top, allow the top panel to slide out to the rear. Then at the front of the machine, are two small switches (PLEASE DO THIS WITH POWER DISCONNECTED). Press both to reset (probably only one needs resetting). Then slide the cover back on and it should work again, but if its like my problem, may cut out after a few minutes of heat. This is a safety feature. If this does not solve the problem, the condensor probably needs emptying. That requires you to unscrew the rear panel, but I didn't do this on my machine (an engineer did) so I can't describe what it looks like!
I hope this helps.
Mat G
June 2007