I thought the valve closed as the temperature warmed?
the TF series ranco sensor is mounted inside the heater box, with even a slight amount of engine coolant circulating in there I can't see how it would ever get cold headscratch

Denny, have you checked the reaction of the valve with the sensor bulb dipped in hot water? I'll hafta dig one out sometime and check

Bill

Moved over to the Passing Lane

"When we tug a single thing in nature we find it attached to the rest of the world" John Muir
"When we tug a single thing on an old truck, we find it falls off" me
Some TF series details & TF heater pics & Rust-a-holics Unanimous parking lot