This kit can monitor boilers as well as solar hot water heaters and includes:

 1 HOBO U12-006 logger
 2 TMC6-HD temp sensors
 2 TMC20-HD temp sensors
 HOBOware Lite software

specification:

Memory: 43K
Sample rate: 1 second to 18 hours, user-selectable
Battery life for U12: 1 year (typical) user-replaceable

Temperature:
Range: -40C to +100C (F)
Accuracy: +/-0.25C

Producing Area:USA