Mr. Heater Gas Valve Problem

"A tap" might indicate just what I was getting at....that something is "on the edge." Might be the pilot is dirty and does not get the thermopile hot enough, and it doesn't output enough power, or that the thermopile is getting old and same thing, OR that the stat wire run is too small or too long, or that the stat contacts are getting dirty

So bypass the stat right at the unit and see if it works. If it does you are on the right track. Clean the pilot see if the flame looks good. IT SHOULD NOT BLOW which indicates a partially clogged pilot orifice. It should be soft and quiet, and might have "some yellow" showing at the tip. If that is the case try replacing the thermopile.

I may have worded poorly.

When you light the pilot and hold down the spring knob, you are manually opening the electrical solenoid valve safety. This is what allows gas to flow an "enables" the valve to operate, when the pilot flame blows out, this loses power and goes shut. In normal operation the thermopile heats up via the pilot, it outputs electrical power and holds that open. But on these "self powered" units, part of the t-pile power also has to open the main gas valve--when the stat calls for heat, so it is an extremely low power delicate device. Any of the causes I mentioned above can stop it operating.