I have a circuit that auto-fills a water tank to around 50% level (+/- a hysteresis band) based on an immersion sensor and some logic (not important for the question).
When auto-filling (low water level detected), a solenoid valve opens (energized) to direct the water into the tank, while the pump is running. When level is restored, both pump and valve is de-energized.
The user can also manually power the pump via a switch to dispense water to an outlet. In this case the solenoid valve is closed so the water flow takes direction to the outlet (not the tank).
Where the water goes, doesn't really matter to the question.
I've produced the PCB and tested it many times (2 PCBs have been on for a long long time with extensive manual pump engaging), without problems. But the other day, a triac on one of the PCBs exploded. It happened when the manual pump was already engaged, then the auto-fill triac mechanism kicked in and also powered the pump.
The question is, can it pose a problem, that the triac can engage the pump while the user has it manually engaged?
I've attached a the circuit (no logic, just the 250V stuff).