Ive disconected the fill loop yet the presure keeps rising so I turned off the stop cock for the hot water supply underneath heater and the pressure stays the same is it the heat exchanger or the expansion tank
if pressure rises with appliance turned off (ie not heating) then you'll be looking at heat exchanger. compact is dual pass main exchanger so cold mains is entering system side somewhere.
expansion vessel would be stable pressure then would rise from say 1 - 3 bar after about 10 mins of having heating on
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