I have done everything I can think of to get my heater to put out heat but everything has failed. I checked the core and the water flows through freely. The valve opens and closes like it susposed to. If any one can come up with anything that I haven't done already. I ran a good cleaner through for about 6 hours. I checked to see if the water goes through the core freely and it does. The heat guage goes up to where it susposed to go. I am going to try a 192 degree thermostat and see if that will work. The only down side with that is over heating the heads and causeing warpage.