Help! My one-year old Takagi Jr used in a radiant heat installation has died. It worked fine last winter and seemed to be Ok this year until we got some below 0 weather. If I turn off elec., wait a minute, then restart, it will fire and everything seems normal. It will run about 1-2 minutes, then quits and shows error codes. Error codes seem to alternate between light flashing 3 times and light flashing 4 times. I've cleaned the flame sensor as mentioned in another post (and damaged the fiber gasket but I think i pieced it back together OK). The only difference between this year and last is that I added a direct vent. I bypassed the direct vent (opened the cover on the unit) and then the unit ran until the thermostat shut it off but now it will not run again. I should also mention that the exhaust vent is dirty with what looks like soot. Hope this is not too confusing and someone has some ideas - No one in my area seems to work on these units.