how to fix immersion heater?

If you have power to the immersion heater and getting no heat at all then either the heater needs replacing or you have a failed thermostat.
If you are competent with a mains tester- test for power on the incoming side of the thermostat. If you have no power-check your fuse. If you have power coming in to the thermostat ,now check the outgoing (load) side of the thermostat.
Do not try to mend a faulty thermostat.
If you have no power- the thermostat is faulty. If you do have power- the immersion heater is faulty

Cladlyn
August 2008