First, make sure you have check the documentation for the products with which you are having trouble. Each product’s web page has a link to FAQs and troubleshooting steps. A copy of each sensor’s booklet can be found at: http://www.vernier.com/support/manuals/

It is also helpful to search our Tech Info Library for Frequently Asked Questions (FAQs):
http://www.vernier.com/til/

More troubleshooting steps can be found at:
General Troubleshooting Tips for Vernier Products

If the issue is not resolved, please contact Vernier Technical Support to discuss and provide as much detail as possible regarding the symptoms.

Online: http://www.vernier.com/forms/support/
Toll-free: 1-888-VERNIER
Email: support@vernier.com

If we cannot resolve the issue via phone or e-mail, we may provide you with a Return Merchandise Authorization number and instructions to send the product to us. To help us quickly repair the unit, please include inside the authorized return package:
     -Your Vernier-issued RMA number
     -A description of the problem taped to each unit
     -Your school name and address

Related:
Does Vernier charge for repairs?