Lieutenant Scott wrote:
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?

start up power for the pumps is quite high.

Everyone does it this way...I guess there is a reason.

The valves have what look like 5A capable microswitches.

Thermostats are much more delicate..well SOME are. Timers also.

I think the rationale is that is not a good idea to have - say - a
motorized valve and a pump in parallel..if the valve goes the pump sits
there pumping into an blocked circuit. Ergo the normal thing is that the
valve is open BEFORE the pump starts..you hear the whirr...the boiler
light goes on..the pump starts,...and then the boiler fires.