you need to drain the water from the boiler cold and heating water, turn of service valves, turn of electric undo the nuts to remove any parts open the valve and replace the washer inside then put it back as u removed it. check the site below its got the manual of the boiler check out section 37 it shows the valve u need to remove and also further down it tells u how to do it.
http://www.solvgroup.com/uploaded_files/File/HALSTEAD_ACE_GCNo.47-333-10.pdf
kash, December 2012
