I recently had to turn off the main valve at my gas meter to cap an old buried gas line to my pool heater that rusted out and started leaking. When I turned the gas back on, the pilot lights for both my water heater and fireplace will not stay lit. I can get both to light up when I push down the pilot button, but as soon as I release it they both go out. Both were working properly prior to turning off the main gas valve. I did go ahead replace the thermocouple on the water heater but it is doing the same thing and I find it hard to believe that it is a coincidence that both appliances are doing the same thing. My gas furnace is firing up normally. What else could be the cause of this?