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01-03-2020, 06:54 AM
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#1
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Senior Member
Join Date: Oct 2017
Posts: 1,937
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Hot water tank fill?
I was thinking about this, this morning. How does the hot water tank fill.
If I gravity fill the tank with a hose does it somehow fill the hot water tank as well? OR, does the water pump fill it up when you run the pump?
Thinking again, lol, when filling either straight into the fresh water tank or direct from city water, does it somehow fill the hot water tank?
I'm thinking the water pump has to do it either way, which means I should get that 10 gallons of water into the hot water tank before I hit the road. I could use a little more weight on that side anyway, RF.
Thank you. 
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Larry & Sheree & KD the CAT
2009 Holiday Rambler Admiral 30SFS Lewis County, Wa.
USN 1964-68, USS LEXINGTON CVS-16
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01-03-2020, 07:16 AM
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#2
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Senior Member
Join Date: Sep 2018
Posts: 1,944
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Quote:
Originally Posted by edge68474
I was thinking about this, this morning. How does the hot water tank fill.
If I gravity fill the tank with a hose does it somehow fill the hot water tank as well? OR, does the water pump fill it up when you run the pump?
Thinking again, lol, when filling either straight into the fresh water tank or direct from city water, does it somehow fill the hot water tank?
I'm thinking the water pump has to do it either way, which means I should get that 10 gallons of water into the hot water tank before I hit the road. I could use a little more weight on that side anyway, RF.
Thank you. |
Unless there's something different about your system, city water should fill the tank. Open the hot water faucet to vent the air, and let the water pressure fill the tank and push the air out until it stops burping.
No need to run the pump, though no harm in it other than a few extra gallons of wear and tear, and loss of that ten gallons from the fresh tank.
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Tom & Jeri
2018 Coachmen Galleria 24T Li3
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01-03-2020, 07:24 AM
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#3
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Senior Member
Gulf Streamers Club
Join Date: Jan 2009
Location: Charlevoix, Michigan
Posts: 611
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The pump or city water fills the HW tank.
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GSMC(SW) U.S. Navy (RETIRED) 1967-10-03 to 1993-11-01
1995 Gulf Stream Scenic Cruiser on Spartan EC-2242 Chassis, Cummins B5.9, Allison MD3060, TST 507 , Toad: 2019 Jeep Cherokee Trailhawk Elite W/Roadmaster tow setup
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01-03-2020, 07:28 AM
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#4
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Member
Join Date: Jan 2008
Posts: 85
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When you fill from city hook up the hot water tank fills first. I you fill your fresh water tank that water only goes into that tank. To fill the fill the hot water tank you have to use the water pump to fill it.
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01-03-2020, 07:41 AM
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#5
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Senior Member
Join Date: Jul 2018
Posts: 3,165
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Quote:
Originally Posted by olly72
When you fill from city hook up the hot water tank fills first. I you fill your fresh water tank that water only goes into that tank. To fill the fill the hot water tank you have to use the water pump to fill it.
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There is no FILLS FIRST situation here. ALL the water piping fills at the same time no matter weather you you use city water or use the pump. You MUST release the Over pressure valve at the top of the WH to fill it with water!
The fresh water tank fills by direct fill on some RV's or by turning a valve while hooked to city water.
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2011 Keystone Sprinter 323 BHS. Port Charlotte Fl/Hinsdale MA. Retired Master Electrician. All Motor homes are RV's. All RV's are not Motor homes.
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01-03-2020, 07:49 AM
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#6
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Senior Member
Winnebago Owners Club
Join Date: Dec 2015
Location: Jacksonville, Fl
Posts: 3,542
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When you GRAVITY fill the water tank the water only goes in to the fresh water tank. To get water in the water heater you'll need to run the pump, and probably open a faucet on the hot water side while doing so to let air out of the tank and lines.
When you fill from the 'city water' hookup, that pressurizes the lines the same as the water pump, so water will go in to the water heater at that point. Again, likely best to open a faucet to let air out.
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2013 Winnebago Sightseer 36V
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01-03-2020, 08:05 AM
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#7
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Senior Member
Join Date: Jun 2015
Posts: 244
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Quote:
Originally Posted by Podivin
When you GRAVITY fill the water tank the water only goes in to the fresh water tank. To get water in the water heater you'll need to run the pump, and probably open a faucet on the hot water side while doing so to let air out of the tank and lines.
When you fill from the 'city water' hookup, that pressurizes the lines the same as the water pump, so water will go in to the water heater at that point. Again, likely best to open a faucet to let air out.
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Agree with this
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01-03-2020, 08:14 AM
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#8
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Senior Member
Country Coach Owners Club Solo Rvers Club iRV2 No Limits Club
Join Date: May 2011
Location: Vancouver, WA
Posts: 37,725
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Water tank fills from either the pump or shore connection.
Do NOT open the pressure relief valve on the water heater and fill the tank full. You need that air bubble in the tank to even out pressure fluctuations and cut down on pump run time. It's the same as your stick house water heater or well pump tank. They all have an air space in them. Read the owners manual to verify my statement.
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2009 45' Magna 630 w/Cummins ISX 650 HP/1950 Lbs Ft, HWH Active Air
Charter Good Sam Lifetime Member, FMCA,
RV'ing since 1957, NRA Benefactor Life, towing '21 Jeep JLU Rubicon Ecodiesel
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01-03-2020, 08:59 AM
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#9
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Senior Member
Join Date: Nov 2015
Posts: 26,825
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Quote:
Originally Posted by Mr_D
Water tank fills from either the pump or shore connection.
Do NOT open the pressure relief valve on the water heater and fill the tank full. You need that air bubble in the tank to even out pressure fluctuations and cut down on pump run time. It's the same as your stick house water heater or well pump tank. They all have an air space in them. Read the owners manual to verify my statement.
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EXACTLY^^^^
Opening the T&P Releif Valve will cause the 'air gap' at top of tank to be discharged/lost.
W/O air gap the T&P can weep during heating cycles---water swells when heated.
Air Gap helps control pressure increases when water swells from heating
City water & Pump discharge supply water to SAME cold water line which then feeds water to WH Tank
City water does it directly
Pump uses water from fresh water tank to supply plumbing system
Open a faucet hot side to allow the air in WH Tank to be displaced and water will fill WH Tank whether using City Water or using Fresh water tank & pump
Generic/basic RV plumbing
 
Air Gap
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I took my Medication today. HAVE YOU?
Dodge 3500 w/Tractor Motor
US NAVY---USS Decatur DDG-31
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01-03-2020, 05:38 PM
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#10
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Senior Member
Join Date: Oct 2017
Posts: 1,937
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You guys are the Best. Thank you. I don't know why I didn't ask this question a long time ago. It just popped into my head.
That's a great diagram Old Biscuit. I will print that one out, thanks.
Mr. D. Did you get your rig fixed up from being stuck? From what I read, a lot of damage happened. Sticky note in my head on that one.
Again all, thank you very much for your replies, much appreciated.
Have a Good One!! 
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Larry & Sheree & KD the CAT
2009 Holiday Rambler Admiral 30SFS Lewis County, Wa.
USN 1964-68, USS LEXINGTON CVS-16
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01-04-2020, 05:33 PM
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#11
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Senior Member
Join Date: Sep 2016
Location: Sarasota, FL
Posts: 5,228
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I just did this today getting ready for the next trip. I do this same procedure before every trip if it's been sitting a while.
I opened the T&P valve to let the pressure out (a little water comes out too) and then removed the anode/plug and drained the tank. Then I used a wand and flushed out the tank. The Anode still looked almost new so I put some anti-seize on the threads of the anode and put it back in.
I then connected my white hose to the spigot, set the selector switch to City Water and turned on the spigot. I put my ear to the open T&P valve periodically and could hear the tank filling. After 10 gals (or so), water started coming out of the T&P and I closed it. IMO there is still the bubble above the T&P - I've never had a problem doing it this way.
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Rick and Larrie Dee
1997 40' Newmar London Aire DP CTA 8.3 (Mechanical) 325 Spartan MM
Bringing her back to her glory.
'08 Jeep GC Overland.
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01-04-2020, 05:41 PM
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#12
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Senior Member
Join Date: Nov 2015
Posts: 26,825
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Quote:
Originally Posted by RKins
I just did this today getting ready for the next trip. I do this same procedure before every trip if it's been sitting a while.
After 10 gals (or so), water started coming out of the T&P and I closed it. IMO there is still the bubble above the T&P - I've never had a problem doing it this way.
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That is KEY......
If T&P is open and water allowed to RUN then Air Gap can be forced out
Opening a faucet hot side will bleed air out and NOT disrupt the Air Gap
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I took my Medication today. HAVE YOU?
Dodge 3500 w/Tractor Motor
US NAVY---USS Decatur DDG-31
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