How to stop the hot water going to a failed under sink shut off valve in bathroom

JamesB2018

I have a Weil-Mclain EG 35 hot water boiler. The hot water shutoff valve underneath the bathroom sink has failed and isn't stopping any water no matter how the handle is turned. I'm not sure I'm understanding the setup correctly, but i.r appears that the cold and hot pipes to that particular faucet run directly off the boiler, and I'm not seeing another plane to shut off the hot water. What am I missing? Is there a way to shut off the hot water that I'm missing? I included pics of the setup.

Jamie Hall

Looks like the plumber may have messed up a little there... looking at the pictures, it looks as though the hot water feed to that sink comes directly off the mixing valve (the one with the black knob labelled hot/cold). If that is so... you will have to go further back in the domestic plumbing to find a valve (if there is one) which shuts off the cold water feed to the coil in the boiler, and the cold water to the mixing valve.

nicholas bonham-carter

You could also turn off the cold water at the meter while you are tracing this out.—NBC

JamesB2018

I have the knife switch shut off on the main line into the house located. So if I turn off the cold water there before the boiler, what am I looking at doing to mitigate any water pressure from the water already in the line and between the boiler and the faucet?

EBEBRATT-Ed

There is a Watts? ball valve with a green handle (trying to read the name on the handle) below your mixing valve (the valve with the black cap) Try shutting the green handle watts valve. I think that is the cold water supply to the tankless water heater

Zman

JamesB2018 said:

I have the knife switch shut off on the main line into the house located. So if I turn off the cold water there before the boiler, what am I looking at doing to mitigate any water pressure from the water already in the line and between the boiler and the faucet?

If you turn off the water to the house, you should be able to replace your valve. Since water is liquid, it cannot be compressed. Turn off the valve, drain the water, make the repair, turn the water back on.

JamesB2018

I'm out of the house today, but I'll implement these suggestions when I get home and report how it went.

JamesB2018

Those 2 knife switches did the trick. Was able t install repair valves on the malfunctioning ones under the sink and replace the faucet cartridges and can now proceed with replacing the vanity top. Many thanks!