New water heater shutoff without turning water off

[Anthony21]

A condo has a small drip on the water heater shutoff and really only found out because the water heater will be replaced soon.

The primary shutoff is connected to 10 units. When speaking to one plumber, he mentioned that he could likely add a new shut off without shutting off the primary water. He mentioned capping something, but not much other than that.

Is this possible, is this risky?

Also, one plumber mentioned an expansion tank for the water heater when others did not. Would this be needed if the place has a back flow preventer for the entire place. Not individual units.

Thank you.

 

[Tuttles Revenge]

If the drip is coming from the packing of the water heater shut off valve, then it is likely that the heater could be replaced without turning off all 10 units. But if the drip is coming from any other part of the valve or the valve itself doesn't shut off all the way, that presents more of a problem. If the drip can't be fixed by tightening the packing nut then the water would need to be shut down. When I'm presented with a situation like that, I present a price to replace that valve as an option and give notice that the water could be shut down at that time if needed.. but might not need to if it can be fixed without. Better to give notice and not need it than an emergency or unscheduled shutdown in a condo.

Yes, the water heater needs an expansion tank if there is a device that prevents the thermal expansion from reaching the city water main.. each of them does in that building. They're rated basically by the volume of water that is heated and expanded. So each unit should have the capacity to absorb their thermal expansion even if there are multiple others in the building.

 

[Sponsor]

 

[Jadnashua]

Where I live, to pass a WH replacement inspection, you must have an ET installed even if there's no check valve (yet) installed in the system. If you have one, but none of the other units do, and the building has a check valve, your tank will be trying to absorb the expansion from the whole building. That can be a problem.

Water doesn't compress, so the pressure will rise unless there's some place for it to go. Over multiple units, there's probably at least one faucet, toilet, etc. that leaks, so that can keep the ultimate expansion pressure down...but, if everything is tight like it should be, the pressure will rise while any of the WH is running until someone opens a valve.

Ideally, you'd have at least a unit water shutoff so the whole building doesn't need to be shut off. There are valves that can be installed without shutting off the water and ways to block the water so you can do maintenance downstream, but the easiest thing is to usually shut the main valve off.

 

[Anthony21]

Thank you all!

 

[Fitter30]

The cold water line can be frozen a new valve installed after draining hot water line drained. Have done it many times with liquid co2.