About 1 month ago pilo light wouldn't stay lit so I replaced the thermocouple.. The unit worked fine for about 2 weeks. After that when relighting it would go out after 1 day or so. Bought a new thermocouple and this one would only keep the pilot lit for 1 to 2 hours. Reinstalled the thermocouple I bought a month ago and it now acts exactly as it did before (goes out after a day or so). Is this numerous defective thermocouples or the valve? Also I turned up the pilot gas and cleaned the thermocouple/valve meeting point.

Make sure all chimmey is clear from heater to chimmey. Check the pilot assemble if all is OK then you need to replace your gas valve.