My boiler stopped working last night. I'm suspecting a clogged filter. While I'm waiting for the repair guy to get here sometime today, I thought I'd replace the filter.

Here's my question: I don't see a fuel line shut off....when I take the filter out, how much fuel can I expect to come out of the line? i.e how much of a mess?

Recommendations of dealing with his messy situation? -Harv

umm- if there is no shut off, the entire tank will drain, if it is a gravity fed system.

the boiler is approx level with the tank, and the fuel is pumped, not gravity fed. Still I expect there to be some fuel fed via the pressure created from the volume in the tank (which is very low)

usually there is an isolation valve before the filter. This valve has a spring in it that makes it normally closed. It is kept open by a small fabric wire that is attatched to the ceiling. This is inplace in the event of a fire, and allows for the system to fully contain the fuel to the tank. If you do not have this valve your heating system is not to code and any service company will not work on it until this valve is installed