could be a silver hose under the boiler, trun on valves on it ( might be one or two) when dial reads 1.5 trun off.
If no hose look under boiler to the right can you see a small pipe with two valves on ? turn both on as above.
erj
December 2010
I can answer this question...
re-pressurise a potterton promax system 24 he plus ?