Resideo TDV-040/U 1/2 in NPT Connection Tridicator with 29/32 in Stem

The TDV-040 is a tridicator from Resideo (Honeywell Home), 1/2 in. NPT connection, 3 1/8 in dial.

A tridicator puts temperature, pressure and the relief set point on one dial, which is the whole diagnostic of a boiler in a single glance. Pressure tells you whether the expansion tank is doing its job, temperature tells you whether the boiler is making what the control asked for, and the marked relief point tells you how much room is left before something opens.

Pressure climbing as the boiler heats and falling as it cools is an expansion tank that is waterlogged or wrongly precharged. That reading is the cheapest diagnosis in hydronics and it needs a gauge that works.

Reads 60 °F to 320 °F and up to 75 psi.

• Brand: Resideo (Honeywell Home)
• Manufacturer Part #: TDV-040/U
• Type: Tridicator (temperature and pressure gauge)
• Connection: 1/2 in. NPT
• Dial size: 3 1/8 in
• Stem length: 29/32 in
• Temperature range: 60 °F to 320 °F
• Maximum pressure: 75 psi
• UPC: 085267833783
• Category: Temperature & Pressure Gauges