Thermostat controls water temperature and shuts off heater at target. If broken, heater may heat water to 90°+ (burn risk) or stay on uselessly (energy waste).
See if any of these signs match your device — each one increases the likelihood of this fault.
These are the causes we encounter while repairing Water heater thermostat broken — ranked from most to least common.
Mechanical bi-metal thermostat dead
Electronic NTC thermostat wrong
Thermal cut-out switch failed
Sensor covered in scale
Cable damage between thermostat and heater
Electronic control board
Any of the following = a danger signal — call now and don't try to fix it yourself.
On-site diagnosis, clear pricing before any work, and a documented 6-month warranty.