I do have a block heater. I am also wondering if I should by pass the pump that is between the heater core and the monovalve. I do feel it spinning though, so maybe not, perhaps just a pull and clean. I did contact the seller and have another monovalve shipped out which was completely different from the first one in terms of how it looked. It was slightly different, however, it arrived and already had a torn diaphragm, so I contacted the seller again and should have another shipped out soon. If I could take them apart I could have a good one possibly, but I hear it's nearly impossible to put back together.