Mystery valve on water heater?

Vacuum breaker?

Back up and take another picture so we can see where the lines go.

Does that 1/2" line run outside to a hose bibb or likewise? If so, then that valve is a vacuum breaker that prevents potentially contaminated water from being drawn into your plumbing from the outside. If the pressure in the line drops to less than atmospheric pressure, then it will draw air into the system.

Nice pipe support and wiring to the HWH. Moe? Larry? Curly? or all three? :huh:

Looks like a check Valve to me to allow water out only. There should have been a Ball valve with a bleeder outboard of the check if you get freezing temps.

Also, it actually appears that your main waste line is pitched wrong, back toward the Y, but that could be an optical illusion. Put a Torpedo bubble on it, and get back to us for curiosities sake OK?

Ayuh,... I don't think that pressure relief valve is legal, nor Right either...

It should be plumbed Down, to the floor, 'n Not Up, 'n to the outside...

corey3589 said:

On the cold water inlet, before the shutoff valve, a drain tube that runs outside has a pressure valve inline between the main supply and outside. Is this needed? And why? The valve is leaking cold water outside and needs replacing.

Click to expand...

Pretty sure it's a vacuum breaker Take your picture to a plumbing supply house and ask for a replacement part. Installation is pretty straight forward if you can get the exact same part. IMO not worth rebuilding- if you can

I'm not convinced that is a vacuum breaker. It looks like it could be a shut off valve.
If it is a vacuum breaker then it will not be the source of your leak. All it does is prevent contaminated water from being sucked back into your potable water system.

Bondo said:

Ayuh,... I don't think that pressure relief valve is legal, nor Right either...

It should be plumbed to Down, to the floor, 'n Not Up, 'n to the outside...

Click to expand...

Although not the preferred method- it is legal here and apparently there too. T&P will release to the outside assuming there is no floor drain or sink to receive discharge in the basement.

After you check the pitch on that waste pipe send us a picture of where that t&p is discharging.

It's a vacuum breaker. Reason behind it is to prevent water contamination. If there was a fire somewhere in the neighbourhood and firefighters had to use a fire hydrant, a city main broke, etc, there would be a big pressure drop in the city's pressure- water goes high to low pressure- it would siphon your hot water tank into the citys water supply.

Wait a minute. Does that line with the valve thingy just run to an open end outside?

BC Plumber said:

It's a vacuum breaker. Reason behind it is to prevent water contamination. If there was a fire somewhere in the neighbourhood and firefighters had to use a fire hydrant, a city main broke, etc, there would be a big pressure drop in the city's pressure- water goes high to low pressure- it would siphon your hot water tank into the citys water supply.

Click to expand...

The story was told to me this way: If there was a fire somewhere in the neighborhood and firefighters had to use a pumper truck, the suction on the line could collapse (shrivel) your hot water tank if you did not have a vacuum breaker.