Boiler Pressure problem?

Hi all. After a 10 hour blackout here at -20 celsius, my old boiler won't get up above 8psi and the relief valve has a steady stream of water coming out of it. Suffice to say, 8psi isnt going to get water up to three floors of rads!

I have reviewed the info here and on other sites and believe it is a faulty valve. My question is what are the steps to safely replace the valve. I tried to reseat it to no avail.

So...I picked up an exact replacement today and from what I have read all that is involved is

Power off to the boiler. Shut off water to the boiler. Shut off zone supply. Drain the boiler till no pressure and below the relief valve level. Replace valve. Turn water back on. Turn zone supply on. Turn power on. Then spend a whack of time bleeding rads.
Make sense? Anything missing? Thanks.