Drain boiler from drain point open air vent to rads ,close air vents on rads when refill ,turn of main water supply to boiler when you open cover on left hand side you will find sensor orange pull out pin to get out sensor dis connect wire ,replace with new one ,make sure push pin in right location as you have noticed when taken out ,refill from filling loop build in on right side under ,open nob ,air out all rads ,job of plumber
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