Hi, I want to check my pressure in my expansion tank, can this be done accurately without draining boiler or reducing pressure.As I am about to put Fernox F4 into system, due to untracable leak, the perssure now stands at 0.5 bar, and does not go below.So can I assume pressure in tank should read 1.5 bar to be correct? 1+0.5.Or would I be better off reducing preesure to 0, before checking pressure.also, as I am putting F4 into system that has NO inhibitor in, not for last 15 years,would I gain by adding some at same time as F4, later when/if leak is sealed, or not at all, without flushing first?OR not at all per se;