Get the manual out and look it up??
Or ask here http://www.justanswer.com/sip/Belling?r=ppc|ga|5|HI+%2D+Appliances|Belling&JPKW=belling%20manuals&JPDC=S&JPST=&JPAD=6039509328&JPAF=txt&JPCD=20091204&JPRC=1&JPOP=Omar_sipRevamp_Tagged&gclid=CKW_9s_02qUCFYUe4QodD0Sjjw
Belling technicians on line!