Hot Water Tank - missing Pressure relief valve?

Here is a pic of a hot water tank - ( forget the junk on top - the only plumbing is the red pipes - the rest is private owner junk)
I am acustomed to seeing a pressure relief valve and a down pipe from the pressure relief valve to the drain pan. Is it perhaps that red vertical extender with black knob?

Any ideas anyone?

Reid 306.jpg

I don’t see a TPR valve, but the picture is not great - they are usually installed on the side of the tank.

That black thing you are looking at is a vacuum relief valve.

Water Service Vacuum Relief Valves are used in water heater/tank applications to automatically allow air to enter into the piping system to prevent vacuum conditions that could siphon the water from the system and damage water heater/tank equipment.

There was no other pipes other than the red PEX - and no pipes down the tank on the sides or back.
Anyway wht would happen if there is no PRValve?

I dont see a drain pipe or valve on the tank, but it could be on the back side. If it is, the termination point should be visible, but not like the one below, which terminates into the condenser unit slab.

2118 NW 135 Terr Miami(McKinnis) 033.jpg

BOOM !:shock:

If the thermostat had a runaway condition the tank could explode IF there is no TPR. There simply is no other way to release excess pressure under the right conditions.

Thanks everyone - WOW!
So this could be serious - the sale did not go through for other reasons - guess I should inform the sellers realtor of the potentially explosive situation. (I know they are going to say I am alarmist- “…but tank is already three years old and works like magic…”

I’m not convinced the black knob item above the tank is a vacuum relief. Why would you want to enter air into the tank? Never seen any reference to a vacuum break on any water heater information I’ve read. Did you get a close look at the black knob thing?

some jurisdictions require a vacuum breaker on the water heater.

It consists of a brass body construction with NPT male inlet connection, and a protective cap. Series N36 has a low profile design, is tested and rated to ANSI Z21.22, and is CSA certified. It is suitable for low pressure steam and water service, and is ideal for use in domestic water heaters and supply tanks, table top heaters, jacketed steam kettles, unit heaters, low pressure steam systems, and steam coil heaters. Maximum Working Pressure: 200psi (14 bar), Maximum Steam Pressure: 15psi (103.4 kPa).

Is pex ok there?

Good point Mark.

I got this from the PEX web site:

Install a minimum 18-inches of metallic or other approved material
piping between water heater and PEX tubing.

So I would say that has to be repaired as well.

Good eye !

yes, Pex, seems acceptable here. small island community. seems more lax here than in the Vancouver area.

  • and, NO, there is no Pressure valve anywhere on this 2004 manufactured hot water tank -

would the vacuum relief valve do the job of the PRValve? Seems different functions to me.

did you by any chance move that black box in the middle of the two pipes. i see a lot of relief valves there, actually mine is there. which island comunity are you in?

It still needs a break of 18" between pex and tank - usually copper piping on tank then connected to pex 18" out

I wasn’t there and I wish we had more pictures or a model no. to look up where the TPR tap is on this tank.

Having said that, look at the enhanced picture below and see if you see the “missing” TPR.

A return trip to the property to verify it’s existance may be in order. IMHO.

TPR Mystery.jpg

1 Like

No, two different functions.

I noticed that too, it is highly unlikely this tank is missing it. I think you missed seeing it.


I have seen them totally missing. I did a foreclosed property recently that had a 50 gallon electric covered in insulation. I felt all around the tank and could not find one on the side or the top. I just called it out and moved on.