hi the isars have a filling loop attached to the pipes coming into the boiler. it can be a knob or a screw its a silver braided flexible pipe attached from one pipe to the other pipe sometime there is one knob to turn sometime two normally one on either side of the flexi pipe. if u are confused. type in screwfix tee filing loop in to google and u will see a pic of what it should look like
kash
July 2012
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