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There is a Reliance 640 dort 40 gallon water tank installed in my bedroom closet. It's a mobile home and I rent. It's bad enough that a home model is in there and is larger then a mobile home water tank, but what is worse is there is no drain pipe in the temperature pressure relief valve. I have told my landlord this needs to be fixed and it hasn't. I would like to know how one can tell if there is too much pressure in the tank or when it's getting ready to blow? I'm afraid one night, I'll be asleep and the tank will explode and kill me. There is also no drain; so if it leaks then water will go all throughout the closet and bedroom etc. Is it bad to turn the hot water tank off when not in use? If I take a shower and do dishes once a day... can I turn it off for the rest of the day? It's hooked up to a holding tank which is hooked up to a well. Is this considered a closed loop that needs to have additional pressure relief?

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Water heater explosions are extremely rare.
I do water heater research including insurance data on water heaters >>> the insurance industry has no reports that I've ever seen of exploded water heaters.
The water heater manufacturers experimented on prior generations, so now our water heaters are safe.
You can turn the water heater off when it is not being used.
You can also set the temperature to a modest 120 degrees and then the water never gets hot enough to cause any problem with the TP valve (drain pipe) or any problem burning you when you use hot water.

If you have a gas water heater, the TP valve will start dribbling water if there is ever a overheating event. So you will see it starting to get bad and then you can report the problem to your landlord

If you have a electric water heater, electric water heater has 3 safety features.
1) The circuit breaker
2) An energy cut-off red reset button located behind the top panel.
3) The TP valve

Here's another solution. Put a metal paint can or metal pot under the TP valve pipe where it comes down to the floor. Do not cap off this pipe.

My last solution is one my friend took when draining his water heater in a rented trailer. He drilled a hole in the floor. Your TP valve should exit the trailer. His solution might not be right for you. But take some photos of the problem and keep them in store in case the landlord refuses to refund the deposit.

Rest well. Every trailer, and every home has a water heater. I worked in the trades for 30 years. I never saw or read of one exploded water heater except the mythbusters video on U-tube (which is entertaining and shows how far a water heater has to be pushed before there is a problem).

Posted on Nov 02, 2010

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Hot water tank wont heat water, how do you relight or resat, its a reliance self cleaning 808

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Welcome to the Reliance Water Heaters Owner's Manual and Installation ... 9 40 EKRT - 40 Gallon Tall Self-Cleaning Electric Water Heater - 9 Year Warranty . ..... 10 50 DHPST - 50 Gallon Electric Heat Pump Water Heater - 10 Year Warranty .

How to light the pilot on a Reliance 606 water heater ...

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Reliance Water Heaters - Consumer Affairs > Homeowners > Bath & Plumbing

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I purchased a Reliance 606 water heater in 2010. ... That they don't TELL you there's areset button or that I'm having conspiracy thoughts ... After several attempts, I was able to relight it. ... It's heading to the junk pile and I will purchase a new reliable (NotReliance) ... Checked breaker and changed breaker still no hot water!

Dec 28, 2015 | Reliance Water Heaters

1 Answer

Reliant 40 gallon tall electric water heater replaced both thermostats upper and lower elements flushed tank hot water very hot temp turned down lowest possible keeps tripping reset button what else could...

Problem has to be bad element or bad thermostat.

Test elements for short to ground through metal tank wall:

Make sure factory-installed insulation and cover are re-installed over new thermostats so they do not misread tank temperature.
If problem does not show with elements, then replace thermostats again.

If you need further help, I’m available over the phone at

Oct 06, 2012 | Reliance & 40 Gal Electric Mobile Home...

1 Answer

I have a model 640 Reliance water heater. SN # A07A150454 M,F, 01/30/2007. About 3 months ago the water started getting cooler, then won't start. I turn the control up, then it starts, but the...

I believe 640 is typical tank-type atmospheric-vented gas water heater.
Gas water heater problems can get complicated. New heater sells for $350 at local box store.

If thermostat is not controlling temperature accurately, then (1) gas control needs replacement (2) water heater has sediment build-up (3) combustion and burner parts need cleaning. (4) All three things above, plus additional causes such as bad venting or not enough combustion air.

Usually recommended that plumber replace gas control valve thermostat:
See typical tank-type thermostats:

Clean sediment out of tank:

Clean combustion chamber and burner parts and troublehoot venting and air supply:

Aug 07, 2011 | Reliance Water Heaters

1 Answer


Reliance is AO Smith company

Age of water heater is on serial number located on label on side of tank. First digit is letter, next two digits are the year. So C04 is 2004. Label also shows wattage of elements inside tank.

606 water heater at Reliance

PDF spec sheet below shows your tank takes 4500 watt element.
I buy ordinary screw-in type 4500 watt elements for $20 at Lowes, I can't remember price exactly because they're inexpensive.

Typical 606 manual:
Shows element and cleaning/replacement page 20.
We know your lower element is burned out because plumber checked and said problem is element.
We know upper element is working because you have some hot water.
If upper element is bad, then tank has no hot water.

Photo from manual shows typical element that I buy at Lowes or hardware store:
Manual does not mention special element required.
Your element burned out probably because sediment is built up inside tank, and not because stock elements are inferior.
Is your electrician/plumber also going to clean sediment out of tank?
Changing element and cleaning sediment will restore full efficiency to your tank.

Here are step-by-step images that show do-it-yourself, so you can see if this is correct project for you:
Page shows how to drain tank, replace element, and has links to troubleshooting if you want to test parts and learn more about your water heater.
Also see:


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I have a 40 gallon electric reliance water heater model no. 8 40 2ARS8 - serial no. M94566434 that I need dimensions for so that we can replace it with a new model. Thank you.
Reliance is an AO Smith company
Link above goes to Reliance electric water heaters
I cannot find your model number
The serial number seems to show it was made in 1994, so the spec sheet would be difficult to find
You must have bought a good heater and taken care of it for it to last that long.

Typical 40 gallon Reliance electric:
18" x 59-1/2"
20-1/2" x 44"
Self-cleaning type Reliance 40 gallon
19" x 60"
21-1/2" x 46"

The size of your heater can be determined by measuring the height, and then measure across the top to get the diameter. Your measurements will be close to the numbers shown above.


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Keeps triping red reset button 640 dors

More than likely it needs to be replaced if you have to constantly reset it. Shut of power and repalce thermostat, it just snaps in place and easy to remove.

Sep 02, 2010 | Reliance & 40 Gal Electric Mobile Home...

1 Answer

My Reliance 606 40 gallon water heater only heats up enough hot water to fill a bathtub. We've drained it, the pilot light is fine, it heats up the water really hot, but it just doesn't seem to be able to...

How big is your bathtub? Is your water heater set on the hottest setting? What is the temperature of the hot water at the tap?

Keep in mind that hot water can cause severe burns. Children and those with diminished mental capacity can be seriously harmed by hot water.

The "40 Gallon" rating on the water heater is usually the amount of hot water the unit can produce in one hour. So the tank, and the amount of immediately available hot water, might be smaller than 40 gallons.

My bathtub is 2 feet wide by 1 foot deep and 4 feet long. This is 8 cubic feet or almost 60 gallons. So a 40 gallons of water at 120 degrees, mixed with 20 gallons of cold water (60 degrees), fills the tub with 100 degree water. My January cold water is 42 degrees, so it will take 40 gallons at 129 degrees to fill the tub. If the tub is cold to start it will take even hotter water.

So the water heater might be just fine.

Possible solutions:
1. turn the temperature up on your water heater- or the temperature control could be malfunctioning and not getting the water hot enough.
2. insulate your hot water pipes so that the water loses less heat on the way to the tub.
3. bigger water heater.
4. smaller bathtub, or less full bathtub.


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