Can someone tell me what are the correct wires from an Immersion Heater switch to the thermostat. The thermostat will not heat the water although a current is passing into it
If you have an immersion with an internal thermostat the live goes into the thermostsat first then out of it onto the live terminal the neutral and earth have their own separate terminals.
Sounds like your thermostat is knackered.
It could be that the immersion heater has gone open circuit. By this I mean that the coil has been immersed in water for a number of years and that corosion eats in to the metal and the element breaks
The only course of action if this is the case, is to drain down the cylinder and replace the complete element including the thermostsat, as this could have been subjected to fault currents when the break occured.