[darsunt]

As I understand it, they have changed to code requirements for p/t valves for water heaters in Southern California. The new p/t valves have no relief pipe. Instead the gas line runs up to the p/t valve first, then back down to the burner below. If the tank overheats. the gas supply is shut off.
The only actual relief valve is attached to the water supply coming in to the house, the tank pressure will back up into the water supply and pop that valve outside.
This system (now required) seems very complicated, unreliable. I can see terrible things happening if things go wrong. What do you guys think?

 

[darsunt]

This strange code apparently applies to water heaters inside the home, not water heaters with outdoor access

 

[joed]

First I have heard of this. Glad I don't live in California.

 

[TheEplumber]

I first heard about this roughly 5 yrs ago from a plumber who moved to my area
What terrible things do you see going wrong?

 

[Ghostmaker]

If the gas is shut off the over heat condition is resolved. The other benefit is no water is wasted dumping out to the floor. If either method of safety fails end result is the same tank explodes. Nothing made by man is fool proof.

What do they do with an electric hot water tank kill the power?

 

[ddawg16]

Actually, it makes sense.

The valve is mechanical....so I don't see it being any more complicated than the typical PT valve.

 

[darsunt]

If both valves fail then the tank explodes or large sections of the water supply system blow apart.
If just the gas valve fails the pressure in the water supply lines might still do much damage before the other valve opens.
The gas valve itself seems like a vulnerable leak point.
If the outside valve malfunctions under normal water pressure huge amounts of water could be wasted.
Maybe it is not as bad as I my initial impression. But it does seem like a complex system with more potential of things going wrong.

 

[Ghostmaker]

 

[AllanJ]

If both valves fail then the tank explodes or large sections of the water supply system blow apart.
If just the gas valve fails the pressure in the water supply lines might still do much damage before the other valve opens.
The gas valve itself seems like a vulnerable leak point.
If the outside valve malfunctions under normal water pressure huge amounts of water could be wasted..

The traditional relief valve on the tank opens under either overtemperature or overpressure.

The relief valve outside the tank is supposed to open under pressure in the same manner altbhough it is too far away to respond to overtemperature.

The pressure sensitivity should be low enough so the plumbing system does not blow apart but high enough that tremendous amounts of water are not wasted.

If you are concerned about pressure relief failure, you can install two pressure relief valves anywhere in the system while installing the new style gas cutoff valve in the single tank opening for a relief valve.