Do I have to shut off my gas hot water tank if the main water supply to my house is off?

It depends what sort of boiler you have..!. Do you have a combi-boiler that relys on water refilling it from the mains supply, in which case.. yes.. once your tank is empty your gas cannot remain on with an empty tank.

If your talking just for a few minutes or so and there is ample water in your tank ,then it will be OK as long as you don't empty the tank.

If in doubt turn it off and reset it when the water supply is resumed for safety sake

Hi Kayak...

If I understand you correctly... then, NO... no need to shut cold water inlet into water heater if the main water supply is shut off to the house...

HOWEVER... you do need to shut the gas water heater gas valve dial down to pilot or vacation setting if the main water supply will be shut down for very long... ok (see picture below)...

Here, want to turn the dial so that it lines up with vacation setting as in the picture below... or may say PILOT on yours. The idea here is to turn the dial on the gas valve to its lowest setting... which will only allow the pilot to remain lit (water heater won't fire off to heat water).

If going on vacation for an extended period or home will be vacant for awhile then it may be best to shut the gas shutoff OFF and then turn it back on and light the pilot when you return... ;)

Let us know what you think...

MARK

No, you don't have to. Your boiler has thermostat. If it gets hot, it simply won't fire.

Why would your main water supply be shut off for your house, do you go on vacation or you doing any repair in the house, if the water supply is shut off to the house there is no need to shut off the water inlet to water heater, just follow Bob's instruction and you will be OK, Thanks.

John