I have a peerless boiler in my home that will not keep a pilot. I've changed the thermocouple with a universal?

one. I've held the manual gas on down for over a minute. I've even removed the one end and tried heating the element with a candle to activate the valve(?). Still no pilot hold. I'm reluctant to buy the mixing valve(?) b/c I fear cost. It's only 8 years old. What am I doing wrong?