Reply To: using hot water from tank on shabbos

twisted- I wrote a long answer which disappeared in the ehter.let’s try again.

As you write, in england , the hot water tank is in the attic and, when you shut off the cold water intake, the hot water still flows out,as it seeks to level with the source. Same in many apartment buildings, where the water tank is on the roof.

Our hot water tanks here in our houses usually is in the lower level and maybe the level aspect is notb apparent. However, you can google anything to do with standard hot water tanks and you will see that there are no pistons, no pumps anywhere in sight in the tank. So, if are you saying that,when the cold water source is shut off (and you are right to say that the cold water drfits to the bottom, being heavier), the hot water does not come out of the faucets (taps for you, new yorkers), I am skeptical about this. Methinks that the hot water will continue as it seeks to find its level with the original source.

BTW- the expansion tank is only tied to the BOILER for the house heating. Our tanks have individual heating, not tied to the boiler.

As far as your “jad soledes bo”. The fact is that,unless you shut off the thermostat, when the water temperature drops below a certain number, the heating will come on. That, again, may very wlel be a true gromo and not even “psik reisha.”

In conclusion- I think that hot water will continue to flow when the cold source is shut. You do not.