Why does the pilot light keep going out on my boiler?

You might find that the pilot light goes out on your boiler for no apparent reason.  Here are a few common reasons for this fault.

The most common cause for a pilot light to go out, is that the thermocouple needs to be replaced. This is a small probe that extends into the flame of the pilot light, and has a small diameter metal wire that runs back to the gas valve.
    

Another possible reason may be that there is a back-draft down the flue which could also cause the pilot light to be blown out.   If the flue has some kind of obstruction, this may also cause the pilot light to go out because the burnt gases cannot escape.  The gases will build up and extinguish the flame.

A faulty or blocked gas valve is another possibility.  The purpose of the gas valve is to control the flow of gas into the pilot.  If the gas valve is blocked, then the flow of gas to the pilot light will be reduced or stop altogether. Sometimes, the gas valve fails altogether.