I have an old gas wall heater that doesn't want to come on. Last year I had the same problem and replaced the valve, thermocouple, and thermostat(twice) and finally go it to work. This year I go to light it and it is doing the same thing. If I tap on the valve with a screw driver it will come on but not with the thermostat, the same thing it was doing last year. I have replaced the thermostat batteries and ran a new temp. thermostat wire and still the same thing. Any ideas? I am at a loss here.