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Old 07-31-2021, 10:14 AM   #1
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Temperature and pressure relief valve

I had to replace a very leaky temperature and pressure relief valve from my Atwood Water heater model GC10A-E. The dealer I bought it from sold me the identical one except for the length of the temperature probe. The OEM was longer by a couple of inches than the replacement. Everything else was identical (pressure rating and temperature rating). Does anyone know if the length of this little white probe will be a safety issue or any other issue? The heater does not leak anymore from this valve and it seems to be working okay, but I am a little bit gun shy and only turn the heater on for 30 minutes at a time. The electric stopped working years ago but the propane gas always worked great. Thanks👍
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Old 07-31-2021, 11:30 AM   #2
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No issue as long as the end of the probe isn’t bound against the tank in some way. Easy to test -

1. remove the new P&T
2. Take a piece of wire and measure the length of the new P&T from the end of the probe to the top of the threads (what would be seen when the T&P is installed) on the body of the T&P
3. Using the wire with your thumb at the measured point at the threads, insert the wire into the port on the water heater at the same angle as the valve is screwed in, up to the point that your thumb hits the boss that the valve screws into.
4. If the wire doesn’t bottom out, your good to go.

How much longer is the probe anyway?
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Old 07-31-2021, 11:46 AM   #3
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Mr. Mark

The newer probe is shorter, not longer.
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Old 07-31-2021, 12:12 PM   #4
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Not all 3/4" NPT T&P Relief Valves are the same

Temp probe for Atwood use a 4" temp probe

Shorter probe should not be used as it may not reach into the water
Must be in the water to properly sense temperatures

Water Heater Tank has by design an Air Pocket on top of water to help control pressure increases
The Pressure sensing is via the Air Pocket
The Temperature Sensing is via the probe being in the water

4" probe is shortest that should be used

Atwood 90028
Or match up one from Local Hardware
3/4" NPT with 4" probe
Temp/Press are universal-----210*F/150psi
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Old 07-31-2021, 01:18 PM   #5
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Quote:
Originally Posted by Old-Biscuit View Post
Not all 3/4" NPT T&P Relief Valves are the same

Temp probe for Atwood use a 4" temp probe

Shorter probe should not be used as it may not reach into the water
Must be in the water to properly sense temperatures

Water Heater Tank has by design an Air Pocket on top of water to help control pressure increases
The Pressure sensing is via the Air Pocket
The Temperature Sensing is via the probe being in the water

4" probe is shortest that should be used

Atwood 90028
Or match up one from Local Hardware
3/4" NPT with 4" probe
Temp/Press are universal-----210*F/150psi
Old biscuit,

Mine uses the 1/2” NPT. Will that make a difference? The parts guy told me that it should be okay, but he also told me about some oceanfront property in Nevada he was interested in selling too! I have an email into Dometic, who own Atwood now, so hopefully they will reply soon. 🙏
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Old 07-31-2021, 02:12 PM   #6
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Atwood 1/2" T&P uses a 4" probe also
*Same as 3/4" just smaller threads/body

2006 was last year Atwood used the 1/2" T&P
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Old 08-01-2021, 06:47 AM   #7
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Chef Guy. Tell us how you survived the big fire.
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Old 08-01-2021, 09:42 AM   #8
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Quote:
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Chef Guy. Tell us how you survived the big fire.
Moisheh,

I am presently in Cochrane, AB (Wild Rose Country) chauffeuring my wife back and forth to Calgary while she judges a 4 day dog show, but as far as the fires are concerned they are still burning up the province of BC. There has been all day smoke here since arriving, from the BC fires, and there appears no let up in site.

We were never that close to the town of Lytton that had burned to the ground, although it was just a 3 hour drive north from our house.

As far as the new pressure temperature probe, it seems to be working so far, or rather the thermostat is working and keeping the temp steady at 140 degrees with no leaks.

I am going to try and call Dometic again once we get back home just to verify that the shorter probe either will work or not work. I expect that I will have to order the longer probe part as called for in the specs.

But it was probably one of the easier re and re’s I have done on this coach. Wish all repairs were this easy🤗
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Old 08-01-2021, 08:43 PM   #9
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2006 vintage
Uses Common DC to operate Electric & Propane
Yellow wire from Circuit Board goes to DC Relay that when using Electric closes to allow AC to Element
*Bad DC Relay
*Bad AC wires to/from relay
*Bad Element

Unfortunately both the DC Relay and Element are located under the cover on backside of WH Tank
*access can be difficult

T-stat Opens at 140*F/Closes at 110*F for reheat
ECO (hi temp t-stat) Opens at 180*F/triggers FAULT Light which locks out heater functions. ECO self resets at 150*F but OWNER has to reset Lockout by turning switch off/back on (electric or gas)

Thermal Fuse (in clear tubing on brown wire) blows at 190*F due to flame blow back (dirty/obstructed burner assembly)
One time fuse...shuts down all heating functions
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Old 08-13-2021, 07:15 AM   #10
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Update on correct information from water heater manufacturer

Quote:
Originally Posted by Old-Biscuit View Post
Not all 3/4" NPT T&P Relief Valves are the same

Temp probe for Atwood use a 4" temp probe

Shorter probe should not be used as it may not reach into the water
Must be in the water to properly sense temperatures

Water Heater Tank has by design an Air Pocket on top of water to help control pressure increases
The Pressure sensing is via the Air Pocket
The Temperature Sensing is via the probe being in the water

4" probe is shortest that should be used

Atwood 90028
Or match up one from Local Hardware
3/4" NPT with 4" probe
Temp/Press are universal-----210*F/150psi
Old Biscuit,

I finally heard back from Dometic technical department after first touching base with them a couple of weeks ago and they assured me that the shorter probe on the Watts temperature pressure relief valve will not be an issue as long as the temperature and pressure ratings are the same, which they are.

So, anyone replacing the longer OEM probe with the shorter Watts temp/pressure probe should not be concerned. Just match the pressure and temperature ratings and you should be fine.

My OEM probe measured a good 4" while the newer one is half that length.

End of thread!
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Old 08-13-2021, 11:36 AM   #11
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Quote:
Originally Posted by Chef Guy View Post
Old Biscuit,

I finally heard back from Dometic technical department after first touching base with them a couple of weeks ago and they assured me that the shorter probe on the Watts temperature pressure relief valve will not be an issue as long as the temperature and pressure ratings are the same, which they are.

So, anyone replacing the longer OEM probe with the shorter Watts temp/pressure probe should not be concerned. Just match the pressure and temperature ratings and you should be fine.

My OEM probe measured a good 4" while the newer one is half that length.

End of thread!
That is correct ChefGuy! But good you “heard it from the horses mouth”!

Thanks for posting back your findings!
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Old 08-13-2021, 11:44 AM   #12
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Temp sensing is via the Probe
Probe MUST be submerged in the water in order to sense water temp

Press sensing is via the internal of T&P Valve
Press is sensed in the Air Pocket area

210*F/150 psi ratings are standard for water heaters

A 2" probe MAY work....provided water level is maintained at/near the T&P Port level
Water level fluctuates depending on pressure in the tank
That is why a 4" probe is used.......

But Dometic tech gave the big OK..........
Hummmmm wonder why OEM is 4" probe when 2" is OK
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Old 08-13-2021, 12:00 PM   #13
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Quote:
Originally Posted by Old-Biscuit View Post
Temp sensing is via the Probe
Probe MUST be submerged in the water in order to sense water temp

Press sensing is via the internal of T&P Valve
Press is sensed in the Air Pocket area

A 2" probe MAY work....provided water level is maintained at/near the T&P Port level
Water level fluctuates depending on pressure in the tank
That is why a 4" probe is used.......

But Dometic tech gave the big OK..........
Hummmmm wonder why OEM is 4" probe when 2" is OK
Overkill by the OEM? Who knows....I do know that I am always able to get cold or hot water out of the water heater through the pressure temperature relief valve whether or not it is turned on or has not been used for several days, so I suspect that the air pocket is not low enough to prevent water from even the smaller probe from making contact. Escaping water has to be higher than any part of the probe's length as it has to escape at the top of the valve, not the bottom...and cold water doesn't expand like hot.

The Watt's valves are also available almost anywhere, unlike the OEM which is special order.
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Old 08-13-2021, 12:28 PM   #14
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Quote:
Originally Posted by Old-Biscuit View Post
Temp sensing is via the Probe
Probe MUST be submerged in the water in order to sense water temp

Press sensing is via the internal of T&P Valve
Press is sensed in the Air Pocket area

210*F/150 psi ratings are standard for water heaters

A 2" probe MAY work....provided water level is maintained at/near the T&P Port level
Water level fluctuates depending on pressure in the tank
That is why a 4" probe is used.......

But Dometic tech gave the big OK..........
Hummmmm wonder why OEM is 4" probe when 2" is OK
Biscuit for the win Think about it.

Mine was leaking a bit more than it should. I took it out and put it in my ultrasonic cleaner. That fixed it right up and restored proper functionality. It was 22 years old and I figure it's still got lots of life left in it
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