Anonymous posted an answer for this Amtrol ST-120V-C THERM-X-TROL ASME Expansion Tank, 68 Gallon :
"No more hot water coming out Amtrol classic boilermate reads:ER3"
Anonymous posted an answer for this Amtrol ST-120V-C THERM-X-TROL ASME Expansion Tank, 68 Gallon :
"Er3 means that the water is being heated for more than 1 hour without reaching the set..."