Responded to no heat. High pressure switch issue. Found water in inducer motor. Dirty trap. Advised hf3 for cleaning trap and assess from there. Customer accepted. Cleaned trap. Found furnace still wanting to kick off on pressure issue. Found flu termination reduced to 1.5. 80k btu furnace 50 equivalent ft of flu ran. On verge of of needing 3 Flu ran. Presented option hm12 to cut out reducer. Customer accepted. Included trap cleaning under flu repair. Cycled system on. Furnace ran properly in first stage. Switched into second without issue. Running roughly 15 minutes. 7.7%o2. 11 ppm co in flu. 0 in supply. 70RA 128 Sa 58 degree deltat.