I have diagnosed an error in my water heater. A control board is defunct and needs replacement. Unfortunately it is winter now and the replacement delivery will take a week or longer. The water heater still functions properly but trips the circuit breaker of one phase occasionally. Is it still safe to use until the replacement arrives?
It is probably "safe". However, a problem which results in an overcurrent trip on one breaker might be causing damage to the related equipment (heating element, relays, etc.) in a way that doing so repeatedly (even for a week) might result in other parts of the heater breaking. Nearly impossible to tell, especially over the internet, as there are a lot of variables involved.
If it is possible to run the heater with that phase (leg) off, then that may be a temporary solution. However, depending on design that may not work at all, or it may result in the other heating elements running at a higher duty-cycle and cause other problems.
This is one of those situations where a few extra $ for fast shipping may be worth it.