Which thermostat models are compatible with 750 millivolt systems such as a fireplace?

Honeywell offers a variety of thermostats that are capable of working with 750 MV heating systems such as fireplaces. Typically these models are battery powered. Thermostats you find at the retail store will indicate on their packaging whether or not it will work with these type of systems. If you’ve already purchased a thermostat and discarded the package, check the thermostat literature to verify compatibility with millivolt systems.

Why is my TH1100DH/TH1110DH/TH1210DH showing an error message E1? What does it mean?

E1 = Replace the thermostat


Standard Millivolt Heat Manual Thermostat

Thermostat TypeMechanical, Non programmable
For Use WithHeat only systems
IncludesThermostat, Wall Anchors, Screws, Wire Labels
Program ModesManual / Not Programmed
Product Height4.75 in
Product Length2.8 in
Product Width1.38 in
Warranty1 Year
Control FunctionsHeating, Cooling


Owner’s Manual [pdf]: CT50 Series Thermostat

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