Water Heater Relief Valve FAQs-3

Q&A on calorifier, geyser, cylinder relief valve leaks

Soot Near TPR Valve: do I Need a New Water Heater?

Plumber says Sooty Smudge on Water Heater above relief valve shows arcing inside the tank and a fire hazard. Says need new water heater?

A tech came out to fix my garbage disposal. Asked to see my hot water heater ( electric).

Wiped his finger across the top of temp/pressure valve and said the dirt shows “arching” inside tank, and is a fire hazard.

Recommend the entire unit be replaced.

Is this accurate, or a scam? On 2019-01-11 by April

by (mod) - Suspicious technician says need new water heater - or is there a bad oil burner?

April

All this sound strange to me. I acknowledge that an expert appliance or water heater repair person or plumber knows things I don't but frankly I can't make any sense out of what you were told.

WhenI first looked at your photo on my smartphone I could not see the smudge that's visible on a larger screen. And I was more suspicious than now after taking a closer look.

In your photo we see a black smudge above the TPR valve (red arrow)

and we can see where your alert technician wiped a finger - or someone did (green arrow).

An air leak up inside the heater insulating jacket might indeed carry soot from an improperly-operating gas burner or oil burner to this opening where on escape a smudge might be left.

So might movement of dirty or dusty air up through the heater and exiting at this opening for other reasons.

You don't tell me what kind of water heater is installed.

Watch out: if this is an electric water heater, and if wiring is arcking the heater is unsafe and should be shut off immediately. But until we have a closer look at the heater no one can say if it's unsafe or needs replacement.

Watch out: if there is an improperly operating gas burner at your heater the system could be unsafe, risking dangerous carbon monoxide poisoning.

Watch out: if this is an oil fired water heater there could indeed be an improperly-operating oil burner.

The possibilities range from a scam - innocent air movement, to an astute technician whom you should buy a steak dinner - if there is an unsafe burner or unsafe electrical connection or wiring in your heater.

Hire someone you trust to take a closer look and tell me what is reported and we can comment further.

Watts 210 TPR Valve Shuts off Gas Supply FAQs

Tip: Details about the installation, testing, and functions of this device are at GAS WATER HEATER AUTOMATIC SHUTOFF

Why is my water heater gas line piped through a T-shaped Temperature/Pressure Relief Valve? Is it Safe?

The gas line for the water heater is plumbed through a "T" shaped TPR and then to the controller. Is this a safe condition? On 2017-05-16 by Jim

by (mod) -

A pressure temperature relief valve connected by a tee to the gas pipe? That sounds strange, and unless it's a special temperature-operated gas supply control.

Otherwise if someone has done something home made it may be improper or unsafe. If that's the case, I would turn the gas supply and heater off immediately and then ask for an inspection by licensed plumber.

by Jim - It's a Watts Automatic Gas Shutoff Valve on Water Heater

Turns out it's a Watts automatic gas shut off valve mounted in the TPR port. There is a TPR at the main water service where it enters the house.

by (mod) - Watts 210 Series Automatic Gas Shutoff Valve

Excellent, Jim. I know of that control but don't know it well. I'm adding details here.

Here is what Watts says about this valve:

Features Used in gas water heater applications to protect against overheating water in the hot water supply heating system

Automatically shuts off the gas supply to the heater if the temperature reaches 210°F (99°C)

Extended shanks for use with water heaters containing extra thick insulation

Manual reset button to reopen the valve after an automatic shutoff

See these documents from Watts

• Watts 210-5 / LF210-5 Series Automatic Gas Shutoff Valve Installation Instructions [PDF] (at Watts website) local copy saved as Watts-210-Instructions.pdf
• Watts 210-5 / LF210-5 Series Automatic Gas Shutoff Valve Specifications [PDF] (at Watts website) local copy saved as Watts-210-Specs.pdf
  
  Excerpt:
  Series LF210-5 automatic gas shutoff valves are positive-acting energy shutoff for the emergency temperature protection of gas water heaters.
  
  They are self-contained devices independent of all other operating controls.
  
  

Water Heater TPR Valve Location FAQs

Where is the T&P valve supposed to be installed ? Water heater top or side?

My new water heater came without a t and p valve. Does it get installed on top or side of heater?

The side hole is plugged and the top hole is open. On 2019-05-23 by davev

by (mod) - When installing a relief valve, use the location marked by label on the water heater - may be on top or side

On most water heaters the tapping for hot, cold, dip tube and relief valve are marked by a label or a stamping into the steel.

Here is what Watts, a manufacturer of relief valves, says:

For pressure relief only, you can install a plain pressure relief valve anywhere in the system simply because pressure is common to all parts of a system. However, we recommend that you install it as close as possible to the equipment which it is to protect.

We recommend simple pressure relief valves only for unfired storage vessels not subject to possible overheating.

Note: never install a shutoff valve between a relief valve and the tank!

• Watts, 52 QUESTIONS and THEIR ANSWERS [about] HOT WATER HEATERS, EXPLOSIONS & WATER HEATER SAFETY], [PDF] (1973) Watts Regulator Company, 815 Chestnut Street, North Andover, MA 01845-6098 USA Tel: 978.689.6066 retrived anew 2018/10/27, original source: http://media.wattswater.com/f-52qa.pdf

Watch out: in my OPINION you should not install a T&P valve at a more-remote spot like downstream on the hot water piping away from the water heater, because of the risk that someone may install a shutoff valve between the relief valve and the water heater, and of course you should never modify the relief valve in any way - doing so is unsafe.

 

Can I move the Pressure Relief valve from the side to the top of my water heater

I have a side mount Pressure Relief Valve and I need the little bit of room. Can I put it on the top of the hot water heater? On 2017-07-18 by George williams

by (mod) - TPR Valves can be top or side mounted on water heaters but must include a discharge tube pointing down and ending close to floor level

George,

The illustration above shows a Watts TPR valve for water heaters in either side-mounted or top mounted position - adapted from the Watts Water Heater Relief Valve installation manual cited just below.

The temperature/pressure relief valve must have a discharge tube bringing hot water to a safe floor or disposal location - one that remains visible - and the tube cannot be piped "up"

If you can respect those rules as well as the instructions that come with your TPR (PRV in your lingo) you should be OK.

WATTS Series 40, 140, 240 & 340 T&P RELIEF VALVES [PDF] (2014)
Excerpt:
Specifications Temperature & Pressure Relief Valves Each hot water storage heater shall be equipped with an automatic temperature and pressure relief valve to protect the heater from excessive pressure and excessive temperature.

The device shall be certified as meeting the requirements of ASME low pressure heating boiler code and ANSI Z21.22. The BTU discharge capacity of the device shall be in excess of the BTU input rating of the heater. The T&P valve shall be a Watts Series 40, 140, 240 or 340.

Is it safe to install the water heater TPR valve on the hot water supply line?

Is it okay/safe to install the TPR valve on the hot water outlet line coming off the top of the water heater? [ see photo ] On 2021-01-18 by Gina

by (mod) - unsafe, improper TPR valve installation: wrong location, improper drain piping

No, Gina that is NOT a safe nor an approved installation. In my annotations to your photo I note that the relief valve is installed more than two inches above the water heater top and is not installed in the TPR Valve tapping.

The TPR valve needs to be installed in a tapping on the heater itself, near the top or on the top, as provided by the manufacturer; if you give the brand and model of water heater we may be able to find the installation manual that will show those exact details.

Here is an explanation from Watts:

Why must a T&P valve be installed on the hot water line as close to the tank or heater as possible?

Thermal lag is one of the biggest enemies of correct T&P relief valve location. Basically, the hot water in the heater itself is to be protected against excessive temperature and not the water in the lines leading to or from it. In some cases, installing a T&P valve in the hot water outlet line as close to the tank as possible is not close enough for adequate thermal circulation.

If a T&P valve is installed within 2" from the tank tapping by means of a close nipple, satisfactory thermal circulation conditions exist.

However, any further distance beyond this enables unsafe tank temperatures. Our film “Danger, Explosion Lurks”, shows very clearly what dangerous high temperatures can exist in a tank before 210°F is reached at the location of a valve 5" or 10" away from the tank.

Therefore, to overcome the location and distance problem, an extension type thermostat is recommended.

Source:

• Watts, 52 QUESTIONS and THEIR ANSWERS [about] HOT WATER HEATERS, EXPLOSIONS & WATER HEATER SAFETY], [PDF] (1973) Watts Regulator Company, 815 Chestnut Street, North Andover, MA 01845-6098 USA Tel: 978.689.6066 retrived anew 2018/10/27, original source: http://media.wattswater.com/f-52qa.pdf
  
  Watch out: a TPR valve not properly located risks failing to respond adequately to over-temperature or over-pressure in the water heater, risking a BLEVE explosion.
  
  Finally: I'd like to see a photo of that TPR valve and another of its data tag.
  
  Watch out: Looking again at your photo it looks to me as if the TPR valve is connected to a pipe that goes "up" to some unknown destination or "down" to a valve that is closed; this is an unsafe and dangerous and incorrect installation.
  
  Safest would be to turn the heater OFF entirely until the plumbing is done correctly.

Locating the water heater TPR valve on the heater top vs on the heater side

Water heater relive valve on side of water heater needs to be put on top of water heater so it flows down is it hard to change it to the top of the heater so it flows down the out side to the out side of the wall - (Aug 3, 2015) glenn

Reply:

Glenn,

Watch out: you should never pipe the TPR valve "up" at any point;

1. The valve must be mounted on the fitting provided on the water heater as otherwise its temperature sensor won't function properly.

2. The piping must flow only downwards from the valve mouth, otherwise the risk is ultimate clogging of the TPR valve and a BLEVE explosion.

3. IF the valve is taken out through a wall and/or to a location not readily visible by building occupants, in order to know if the valve is leaking (and thus that a dangerous condition exists) install a Tundish fitting (Search InspectApedia for "tundish" to read details).

Do I also need a TP valve on the cold water line? What about a check valve on the cold water supply main line?

Do I need a pressure-relief valve on the cold waer pipe that feeds my hot water heater tank? - Watts

Do I need to install a check valve on the cold water supply main line? Is it safe to do so? - Watts

On a municipal water supply system, do I need a check valve on the cold water line if a TP valve is installed on the water heater? - Watts

Reply: no

No, there is no need for a separate pressure relief valve on the cold water line feeding the water heater. That's because water pressure within the system is common throughout all of the plumbing system: cold water line into the tank, hot water in the water heater, and hot water in the hot water lines leaving the water heater tank all see the same pressure. [10]

... the original purpose of a check valve was to protect the [water] meter by preventing superheated water from backing up into the cold supply main from range boilers and heaters.

However, the very condition that can cause this, can also cause explosions and the temperature and pressure relief valve principle protects against both excessive temperature and [excessive] pressure, thereby eliminating the need for a check valve.

A check valve closes the [plumbing] system, thereby allowing pressure to build up from thermal expansion higher than the city main pressure, and therefore should not be used except where required by local codes. [10]

Note: We add that there are other reasons for a check valve or backflow preventer valve on water systems: to prevent water from the building from flowing backwards into the city supply mains during an interval of loss of pressure in the mains.

Should such a pressure loss occur the risk is that unsanitary water from buildings connected to the mains could flow backwards into and thus contaminate the water supply mains in a community.

Most community water supply systems include a pressure regulator combined with a backflow preventer or check valve at the water meter. Watts' note above was penned in 1973. The company may have more to say on this topic today.

When a hot water system includes a temperature & pressure relief valve installed on the water tank or heater there is no advantage to installing a check valve to protect the water meter - as Watts explained in the quotation above.

Watts points out that if a check valve is installed on the cold water line to the water heater, a result is a pressure rise in the system each time water is heated in the hot water tank.

Water Heater TPR Valve Operation FAQs

Should relief valve lever or handle be in up or down position?

Should relief valve lever or handle be in up or down position? On 2017-01-25 by Anonymous

Reply by (mod) -

On a typical pressure relief valve the handle is "down" when the valve is closed. That would be the normal operating position.

The handle or lever is lifted to test the valve by opening it - to discharge water or hot water.

 

Can you drain the water heater to remove scale through the relief valve?

I have a gas water heater pressure/temperature valve that needs to be replaced. Have you ever drained the water inside the water heater through the pressure/temperature relief valve as far as possible, then remove the valve for a quick change with a new one. I expect some water to run out during the valve replacement.

The water heater is about 17 years old, and probably never had a maintenance draining all that time.

The water heater has a bottom plastic drain valve, and I would rather not go there to drain the water down, knowing the calcium deposits in the bottom could get stir up causing added problems, not to mention the plugging up of that bottom drain valve, possibly getting into the hot water piping running to the sink faucets on startup. (Sept 15, 2016) Gary

Reply: no

Gary the TPR valve will only drain off the water down to the valve mounting tapping; That's close to enough though you can expect a bit of spillage when you remove the old valve.

Also search InspectApedia.com for WATER HEATER DE-SCALE as that operation is in your future - scale removal.

Shouldn't water temperature also be adjusted when installing a PRV?

If the plumber is only installing a PRV and not adjusting heat then isnt that unsafe and not proper?

Its my understanding heat & pressure have to be adjusted? (Sept 8, 2016) Marcy K

Reply:

Marcy:
If street pressure is too high the TPR valve will indeed be likely to spill water as it heats up; this is an unsafe situation for several reasons, risking at the very worst blowing up the system if the repeatedly-spilling valve becomes clogged.

Check the incoming water pressure and compare that with the pressure range your heater manufacturer says they can handle as well as comparing it with the operating pressure of the TPR valve. You may need to install a pressure regulator at the point at which water enters the home.

That's a common repair.

Also see ANTI SCALD VALVES & TEMPERATURE CONTROL / MIXING VALVES for protection against burns from water that's too hot

Should the heating boiler or water heater temperature gauge also be adjusted when we adjust water pressure?

If the pressure is adjusted does the heat/temperature gauge also need to be adjusted? (Sept 8, 2016) Anonymous

Reply: No.

No. The gauge should be reading the actual system conditions.

Water Heater TPR Valve Leaks due to Thermal Expansion FAQs

Tip: see the explanation at THERMAL EXPANSION TPR VALVE LEAKS

Watch out: leaky pressure/temperature relief valves are an important safety concern that needs proper diagnosis repair by a trained plumber or heating service technician.

Hot water pressure increase & leaks in hot water systems

You go through alot of effort to explain how heated water expands and the resulting increase in pressure.

All that is well and good for theory. In a domestic (North American) water supply system, to the best of my knowlege there is nothing to prevent the expanding water/pressure from the hot water heater from just backing up into the supply plumbing and hence the water pressure in the hot water heater would NEVER exceed the supply pressure.

Or is there a required one way valve somewhere in the system I am not aware of say in the hot water heater? On 2017-01-08 by GaryC

by (mod) - thermal expansion occurs when water is heated; unless there is a pressure tank or expansion tank on the system that can cause leaks

Gary a detailed explanation is now found at THERMAL EXPANSION TPR VALVE LEAKS

Please take a look and let me know if question remain

by GaryC - how do I know if my water supply includes a check valve or backflow preventer

OK, Thanks. In that article it said "The water utility supply meter may contain a check valve, backflow preventer or water pressure reducing valve."

Is there a way to tell if my supply meter has a check valve?

I do not see a backflow preventer (other than on my sprinkler system). And by pressure reducing valve I assume you mean a pressure regulator. Will a pressure regulator prevent a backward flow?

Thanks for the great question, Gary.

Typically a check valve is a physically separate device found before or just after the water meter.
On a municipal supply system it will be a (usually brass) device like the ones shown at CHECK VALVES, WATER SUPPLY inspectapedia.com/water/Check_Valves_Water.php

You may see reference to a "backflow preventer" on municipal water systems - illustrated in the article above and also present at heating boilers and perhaps some other equipment.

In addition, yes a water pressure regulator on the water supply system, typically where water enters the building, acts as a check valve: it is reducing higher incoming or city-side water pressure down to an acceptable and safe level for the building, so it's acting as a one-way valve.

Additional pressure reducing valves will be found in the form of a water feeder valve at a heating boiler.

So for example with some made-up numbers, suppose we have a city water supply system that delivers water at 100 psi into a neighborhood water main.
The house water pressure regulator drops that incoming pressure to a safer 70 psi on the house side. So when no water is running in the house you could measure 70 psi on the system (say by mounting a gauge at a hose bibb or washer supply hookup).

In that same house, heated by a hydronic boiler, another pressure reducer/regulator is installed at the heating boiler. That regulator
drops the 70 psi pressure on the house side to 12 psi cold into the boiler. Otherwise the boiler's relief valve (opening at 30 psi) would spill.

On a private well and pump system a check valve may be in the pump body itself (in the face of a jet pump for example) or on piping between well pump and well, or in the well at the piping bottom (a foot valve).

Yes, a pressure regulator prevents backwards flow. However because pressure regulators usually make use of a flexible rubber diaphragm and spring to do their work, they are not foolproof. For example the diaphragm can rupture. So many municipalities also require a more reliable (metal, mechanical) check valve or backflow preventer.

That's because we don't want to risk contamination of the city water supply that could occur during a period of low city water pressure that could permit unsanitary water from an individual building to flow backwards into the city water mains.

Why is hot water pressure going up to 150 psi in my water heater tank?

I had to install a new temp controller in my hot water tank. It is a bourdon tube type and I installed exactly like the original one. The water in the tank is heated by a coil as a separate zone from the furnace. The house water pressure is about 50 psi. I have the tank temp set at 125 degrees.

I installed a pressure gauge between the pressure relief valve and the top of the tank. When the hot water from the furnace enters the tank the water pressure goes from 50 psi to 150 psi and the relief valve discharges a little and then stops. The water temp is 101 degrees at this time. Why is the hot water tank pressure increasing to 150 psi? - Alan

Reply:

Alan you may need an expansion tank on your water heating system. Heating water in a closed container increases the pressure.

See our discussion about THERMAL EXPANSION TPR VALVE LEAKS