Had same problem cured by disassembling switch (two Pozidrive screws under blue cap). Between power leads is another screw with two nylon washers. My 'take' is that this screw is adjusted in factory by a spacer between the washers or their pressure checking supply is faulty (I don't in fact believe they are checked by pressure ?) Testing the switch by finger pressure and a continuity tester I found the adjustment very 'iffy. Either something or nothing ! Switch is sealed and suspect contains an over centre device which is manufactured to trip at,say,20psi. Tuned it to trip at lowest possible pressure and eureka, it works well. There is also a small finned 'spinner' in the void above the switch which I may have disturbed too ? Don't quite see what relays and accumulators have to do with the problem, if the pump has a good supply it will either explode calorifier
, burst pipes or put taps into orbit ! It does not know what is ahead, only the pressure difference between the vanes and the switch diaphragm
? Beware the diaphragm can go in upside down easily causing a leak !