I recently cleared an old ECM giotto gauge that iaindb gave me for free cause it was full of scale. Becuase the pipe is thin, its really hard to find out where the scale is.
The way I cleared mine was to screw the fitting on the end and use it as a bit of a funnel for putting some undiluted descaler down it. I then got a a lighter and ran the flame up and down the pipe to heat it, the scale and the descaler until it started bubbling, at which point I took the flame off, got my unwound paper clip (about 7cm long) to poke the scale, then repeated. You can tell where the scale is by how far down the pipe you have to apply the flame to get the descaler to bubble. When its at the bottom the scale is gone!
Hope that helps if its a scale problem.