Water in the hot water heater

Bobbo wrote:
Water in the water heater is never "PULLED" out. It is "PUSHED" out. What gets the water out is opening the tap reduces the pressure at the outlet of the heater. Then the higher pressure at the inlet of the water heater pushes cold water into the heater, which consequently pushes hot water out of the water heater. If there is no water to push into the water heater, none can be forced out.

ewarnerusa wrote:
I drain my water heater tank by opening the low point drain and opening the pressure relief valve on the hot water tank. All 6 gallons will drain from the low point drain. I'm not sure if there is supposed to be a check valve on the water tank inlet that prevents this from being able to happen

No, there is not. If you have a 1 valve bypass, you will have a backflow check valve at the hot water outlet to prevent antifreeze from back filling the tank when winterized, but none otherwise. A 2 or 3 valve bypass system does not need one. All of those will prevent air from entering your tank when draining through the cold water inlet. That is the reason you have to open the pop-off valve. You have to vent the water heater someway to release the vacuum.

Depends on RV mfg.
Some do install check valves on cold water inlet so higher pressure hot water does not push back into cold water system (hot is higher pressure due to 'swelling' from being heated)

More and more just have a check valve on hot outlet for bypassing water heater.
Mine doesn't have any check valves.......it has 3 valves

So check your arrangement to know for sure

Water in the water heater is never "PULLED" out. It is "PUSHED" out. What gets the water out is opening the tap reduces the pressure at the outlet of the heater. Then the higher pressure at the inlet of the water heater pushes cold water into the heater, which consequently pushes hot water out of the water heater. If there is no water to push into the water heater, none can be forced out.

ewarnerusa wrote:
I drain my water heater tank by opening the low point drain and opening the pressure relief valve on the hot water tank. All 6 gallons will drain from the low point drain. I'm not sure if there is supposed to be a check valve on the water tank inlet that prevents this from being able to happen

No, there is not. If you have a 1 valve bypass, you will have a backflow check valve at the hot water outlet to prevent antifreeze from back filling the tank when winterized, but none otherwise. A 2 or 3 valve bypass system does not need one. All of those will prevent air from entering your tank when draining through the cold water inlet. That is the reason you have to open the pop-off valve. You have to vent the water heater someway to release the vacuum.

Old-Biscuit wrote:
Pump only sucks water out of fresh water tank and DISCHARGES to rv plumbing system (city water ties into same line)
Cold water from rv plumbing system enters water heater tank thru bottom and then comes out top of water heater tank to feed hot water system

Water heater 'capacity' being listed as part of fresh water capacity is a mfg. marketing ploy ------puffering.

True, but it's also telling you how much water to factor in when you are adding your weght up.

brholt wrote:
Some RV manufactures list their freshwater capacity and either include the hot water tank or list the capacity as X + 5 gallon hot water heater.

FWIW, by far the most common water heater tank sizes used in recreational vehicles are 6 gals and 10 gals, not 5.

brholt wrote:
...My question is can the pump actually draw out the hot water if your fresh water tank is empty?

No it cannot. But I drain my water heater tank by opening the low point drain and opening the pressure relief valve on the hot water tank. All 6 gallons will drain from the low point drain. I'm not sure if there is supposed to be a check valve on the water tank inlet that prevents this from being able to happen, but is always how I drain my hot water tank and useful info if I ever found myself in a jam and needed access to that water.

Pump only sucks water out of fresh water tank and DISCHARGES to rv plumbing system (city water ties into same line)
Cold water from rv plumbing system enters water heater tank thru bottom and then comes out top of water heater tank to feed hot water system

Water heater 'capacity' being listed as part of fresh water capacity is a mfg. marketing ploy ------puffering.

No