when can a gas hot water boiler be converted to 2 stages

Empire_2

Is this steam or Hot water? I'm sure you are working with HW....right?

dave w

is it ok to change an old single stage gas boiler to 2 stage

i have came across an national us boiler with a 1-million,500 thousand btu input and model number 7-66
over time this orginal boiler gas fired single stage boiler has been converted to fire at 2 stages by adding a 2 stage honeywell gas valve v89a1626 which has an built in regulator to the manifold.it fires at 3.5 inches water collum high fire and .08 inches water collum low fire.this gas valve is being controlled by a honeywell t775a.the orginal diaphram gas valve is still hooked up with an differential expandsion pilot as a safty.stage one is set to 45-50 degrees.stage 2 is set at 70-68 degrees stage three is set to 72-68 degrees(outdoor reset overide)on the t775.there is an unoccupied switch to change from occoupied .an optional 12 hr over ride timer.my question is,is it ok to change a boiler as this one and convert the boiler with a gas vale and operate it at 2 stages?how do you know it will be safe to do this.will it work on any type of furnace?