Heater thermostat wiring

Discussion in 'General Electronics Chat' started by CrazyAl, Sep 27, 2010.

  1. CrazyAl

    Thread Starter Member

    Aug 27, 2010
    Hi, I have an old heater that I have recently put in one of the bedrooms now it is starting to get colder. I have found that it will not heat up much unless the thermostat dial is turned more than halfway, where it will "click".

    Having opened it up I can see a basic circuit and it looks like the heating element (its an oil heater that plugs into the mains 240v 50hz 1000watt) is in parralel with a varible resistor. I think I have found what causes the clicks, a small screw that is designed to come in contact with a piece of metal shorting out the variable resistor (I could be wrong).

    Does anyone know what this small screw does? and is it just a case of ajusting the screw, thanks.

    some pictures;



  2. mbohuntr

    Senior Member

    Apr 6, 2009
    I think you will find the heater thermostat is "clicking" at the temperature of the room. If you wish it warmer, turn the dial up more, cooler, down. Please do not mess with that unless you are an electrician. There's plenty of current there to kill you, or burn the house down.
  3. CrazyAl

    Thread Starter Member

    Aug 27, 2010
    After doing a bit of testing with my multimeter I have found out there is actually a very high resistance path of continuity between the live and earth terminal on the plug pins for this heater so I have now stopped using it.
  4. BillB3857

    AAC Fanatic!

    Feb 28, 2009
    Glad to hear that you have stopped using it, but since you asked what the small screw is for.....Probably used to calibrate the thermostat. Many of thermostats of this type use a small magnet to keep the contacts closed until the temperature exceeds the point at which the heater turns on by a few degrees. That provides a differential or hysteresis between ON and OFF so it isn't cycling quickly. That would tend to burn the contacts reducing the life of the unit.