Problem
Heat conduction is insufficient to heat sensor head

Cause
The heater’s ceramic insulators may have become dislodged - which often occurs if the heater has been vigorously tugged on.
This will be apparent if the heater no longer sticks when compressed, resulting in insufficient contact to conduct
heat to the retainer

Solution
Gently wiggling the heater back and forth can sometimes resolve the issue. Servicing may be required