Ben Blaukopf wrote:


However, even if the valve is faulty, if the timer is off then the
pump should still be off,

No.

thermostats and timers drive the valve, the valve has the high power
contacts that drive the boiler and pump.

Its perfectly possible for the contacts to weld shut so the switch is
closed, even when the valve has shut.

If the system is wired 'correctly; that is in fact the simplest explanation.

physical chafing and shorting of wires being another option.