There are a number of things that can effect the smooth functioning of electric heaters. Mainly, you will find that it is from bad wiring or connections that have been broken. You can fix most of these issues with some basic common sense repairs, using soldering equipment and ordering replacement parts from the unit's manufacturer. Be sure, before you work on a unit, that it is unplugged from the outlet to avoid electrical shock. You can also check currents and voltages by using a voltage meter while the unit is in operation. However, be cautious to avoid electrical shocks.
The Fan Runs without Pushing Heat
When the fan runs fine in electric heaters, and there is no sign of actual heat coming out of the unit, it is likely the heating coils or something in relation to the internal wiring. These coils are on the inside of the unit and will have to be checked carefully for breaks in the line. The coil creates a closed circuit, one end touching the other and passing massive amounts of current through them, which creates the heat that is blown out by the fan. If there is a broken coil or a snapped spring line on the inside, a handy person can repair this by soldering the two broken ends together with a splint. This can be done several ways, either by soldering a high voltage wire to each of the broken ends, or splinting them together with a wire clamp.
Check the Circuit Board for Shorts
In some electric heaters, the knobs and controls hook into a primitive form of circuit board that helps the unit regulate heat and voltage. You can test these circuits while the unit is on with a voltage meter and locate any breaks in the system. If you have experience with electronics and soldering, you can generally repair these type of breaks by adding a wire connection or repairing the on that is broken. Most modern heaters have replacement parts that can be ordered directly from the manufacturer and replaced as with any electronic device. A voltage regulator will come in handy in this situation, as you can find out where the current is being lost in the system with a few simple tests.
Check for Burnt Out Components
Another thing that can effect the heat output on electric heaters is regulators and the like that may actually fry or burn out. These are a little harder to detect, and again, can be replaced with some soldering work. These diodes help to pass and regulate current as it goes through the required functions of the unit—everything from heat regulation to regulating the current to specific areas of the heater as it is needed. You can simply remove the circuit board and then apply heat to the solder points at the base of the burnt out diode so that you can remove the component from the system. Simply insert the replacement part and solder it into place. Again, most parts can be ordered from the manufacturer directly or you can buy electrical components such as diodes and regulators at any local electronic store.