On Tue, 22 Nov 2011 09:01:47 -0000, The Natural Philosopher wrote:

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.

High power contacts? Surely the current required for a pump and the gas solenoid etc in a boiler are not "high power", and could be driven directly from the stat?

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.

--
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god said:

"The Divergence of the B Field = 0
The Curl of the E Field + the partial time derivative of the B field = 0
The Divergence of the D field = the charge density
The Curl of the H field - the partial time derivative of the D field = the current density"

and there was light, and he saw that it was good and of constant speed.