Honeywell 3 port valve buzzing: I know the reason and the workaround, but what if it stays buzzing when I'm away for a long time?

[stem]

If the motor fails completely, the valve will sit permanently in the Hot Water only position (it's pulled their by a spring when the motor isn't energised) So the hot water will be heated as per the settings of the controls and the hot water cylinder thermostat, but the central heating won't operate at all as the motor won't be able to move the valve to the central heating position.

 

[Harry Bloomfield]

But back to my original question: if the whole thing fails while I'm away, what's the worse that could happen?

Yes, that is awkward, but doable. Mine is at least reachable with one hand, but to make a swap easier, I turned up some longer bolts, with knurled brass heads, so they could be unscrewed without need for a screwdriver.

If the motor fails, rather than jams, the spring should return the valve to the hot water position.