Domestic - tamper fault on Optima Compact | Electricians Forum - Talk electrics and electricals with fellow professional electriciansthe a and t, ot -hold and tamper return are the bell tamper. if thaat clears the fault, it's probably the bell back tamper not making the tamper switch in the bell box. the panel tamper is the spring on the panel PCB. the other way to check the bell tamper is with your ...