I have a six year old craftmaster gas hot water heater whose pilot light goes out . And it had been very intermittently working. When I Light it as long as I hold the button down the flame is blue and as soon as I release the button the flame goes out. I have replaced the thermocouple twice.The first time I replaced the themocouple it seened to work but the flame went out in less than an hour . I Lit it again and it would work for a while .As I increased the temperature selected value it worked to increase the temperature and worked for about 45 minutes ok. Then no matter how long I held down the button the flame would go out as soon as I released the button. I replaced the thermocoulpe again and the it still has the same problem. How much voltage should I get out of the themocouple when it is heated up to temperate ? Could the control valve be bad?
A thermocouple lead should produce at least 20mv of electrical current in order to be strong enough to hold the magnetic valve in the gas control open to allow gas to flow to the pilot burner, any less than 20mv would result in the same problem you are experiencing. If however, once you get the pilot to light and the main burner comes on if the water heater pilot burner goes out immediately once the water has reached the set temperature then for sure your gas control valve is faulty as it is going out on the inbuilt overheat setting. The only cure for this problem is a total gas control valve change. Hope this helps you. Remember – Get a qualified gasfitter to undertake the valve change as gasfitting work undertaken by those not qualified often leads to leaks and fires.
Selgas Services Ltd Craftsman Gasfitters, Plumbers, Electrical Service Technicians