A plastic coolant tank level indicator was used on the early Hydro-Hot models 

• HHE-200-007E and HHE-200-007M
• HHE-500-007E and HHE-500-007M
• ----- AND EARLIER Models

These models are easy to identify by checking the radiator cap.  These models have 'Giant' radiator cap.  Note that the (brass) tank level sensor below will not work as replacemenet.  There is not enough room inside the tank for the float to activate.

    ELX-01G-ML7

A plastic coolant tank level indicator was used on some of these models.  It has been upgraded to mostly brass tank level sensor. 

• HHE-200-008E and HHE-200-008M
• HHE-500-008E and HHE-500-008M
• HHE-200-009E and HHE-200-009M
• HHE-500-009E and HHE-500-009M
• AHE-450-DE1
• AHE-100-03S and similar
• AHE-100-04S and similar
• AHE-600-DE1
• ---- and others

These models are easy to identify by checking the radiator cap.  These models have regular size radiator cap.

    ELE-800-002

An electronic coolant tank level indicator was used on these models

• AHE-450-DE2
• AHE-450-DW2
• AHE-450-DE3
• --- and others

Note that this tank level sensor screws into a 3/8" NPT threaded port on the boiler tank.  ALL other tank level sensors use 1/2" NPT threaded port.

This sensor is no longer available.   Replaced with this kit:  ELE-800-006-FRU

A Fluid Level Conductive Switch - was used on these models

• AHE-450-DE4
• AHE-450-DW3
• --- and others

Fluid Level Sensor Kit - ELE-800-007-FRU

Fluid Level Conductive Switch - ELX-800-005

Circuit Amp (wiring harness) - ELX-AMP-005