Unit seems to work fine (heat & air). Noticed pilot was out recently, relit and was fine for several days. Noticed it was blowing cold air again and noticed pilot out again. Relit, burner ignites fine and cycles on and off fine (pilot remains lit). After a couple of days, pilot out again. Same situation, relit fine, cycles on and off fine. Using Honeywell VR800 gas valve. Thermocouple for pilot seems OK (usually fail open, not intermittent failure). Suggestion?