So, I’m running out of hot water a little sooner than I think I should. I need some experienced plumbing people to educate me a little bit.
I have two hot water tanks in series. The newer one is probably about 40 gallons (I’m at work, so I’m guessing) and it was installed within the last 5 years. The older one is about half as big, so I’d guess it’s around 20 gallons. I’m not sure how old it is. Maybe more than 10 years.
Setup.
The newer, bigger, gas water heater is where the cold water comes in.
The hot water leaves the newer, bigger, gas water tank to the older, smaller, electric water heater. From there obviously goes out to the house.
Question 1
Make sure I understand the mechanics of water heater in series.
Cold water comes in to bigger tank into the bottom of the tank via dip tube. Hot water leaves out the top of the bigger tank into the smaller tank the same way? to the bottom via dip tube? Where hot water then leaves the smaller tank into the house. Doesn’t that defeat the purpose of the dip tube on the 2nd tank since it places hot water on the bottom of the tank? Or since the tank is smaller, is it supposed to be always supplied by hot water from the bigger tank so it doesn’t really matter?
Question 2
How do I go about troubleshooting this?
As I think about how the tank system works, it’s likely I either have a dip tube problem in one of the tanks or a heating element problem in the smaller older electric tank. If things were working correctly, couldn’t I just turn on a tub & shower to all hot, and feel the temp change fairly quickly on the hot water exit pipe of each tank? Likewise It would seem I could see how long it takes the newer bigger tank’s burners to come on. If the dip tube is not broken, the incoming hot water should make the burners come on pretty quick; unless there’s something wrong with the thermostat.
There you have it. Based on the above what information can you provide me?
If you are running out of hot water, my first guess would be that the pilot in the upstream heater has gone out, so it is doing nothing, and you are only getting hot water from the little one.
While I don’t know for sure what is causing the problem, the inlet on both heaters needs a dip tube. As the water sits, it will stratify, with the hottest water at the top, and coldest at bottom. When you use hot water, it is supplied from the top, and replaced by cold water from below. In the case of the second heater, it is pre-heated water from the upstream heater, until you have used that up, then it is cold, as it would be if the downstream heater were all you had.
The thermostat that controls the heater is near the bottom, So that kicks on the heater as soon as you use a little bit.
Two tanks in series is the same deal, but the downstream tank doesn’t get cold water until the first tank is depleted.
Feeding the small tank from the big tank - the water going into the small tank would be hot already, so essentially the presumably less efficient small tank rarely has to heat purely cold water. It just maintains the temperature.
you could set the temperature in the small tank higher - then you could get hotter water, but when you start to run out, you have another 40 gallons of slightly less hot water. However, I think they suggest that unless you are OK with the risk of scalding (no small children or infirm elders in house) keep all hot water below about 135F
So set small to 140, large to 130. Less energy wasted since you are not heating 60 gal to 140, but enough hot water when you need a bath. Most of the time when you use hot (dishes, hand washing, laundry) you never go beyond the initial 20 gallons.
The (electric) hot water heaters I’m familiar with (IANAP) have a heater element at the bottom and another half-way up. When I found that the shower went cold after a short time (5 to 10 min) it turned out the bottom element was dead; of course, unless you needed a lot of hot water, the mid-level element was enough - for dishes, for laundry…
Does the gas heater have a standing pilot? Is it Lit? If electronic, is it working? Turn the thermostat up and see if it kicks on.
Then check that the large tank is set to “ON” and not “Pilot” and that the thermostat is set properly and not on a setting such as “Vacation”.
Then check the heaters on the smaller tank, disconnect to line to each element and use an ohmmeter to check for an open circuit.
If you have hard water, lime will build up in the tanks that can have an adverse effect on operation.
Before using any water. go out to where your tanks are. Fill the inlet to the tanks then the outlets.
Inlet on first tank should be cold. Outlet hot.
Inlet on second tank hot. out let hotter.
This first test is kind of a weak test.
Now open a shower to hot. Do the same test.
If same results the good. But if outlet of 1st tank temp drops rapidly there may be a problem with 1st tank. If the outlet from 1st tank has dropped and outlet of first tank is also dropping this tank may also have a problem. But if at first everything stays warm then.
Have someone take a long shower, (I live in California and can not advise wasting any water, so use the test water.) AS they are taking a shower notice when the temperature drops. Is either heater heating the water.
If the gas heater is giving out cold water check to see if the burner has ignited.
If along with the gas water heater not giving out hot water also check to see if the electric heater is consuming any electricity. You will need a amp prob to test.
If you have to spend money on this system, I suggest that you replace it entirely with a continuous flow boiler. That way you will have unlimited hot water when you need it and not have the cost of storing hot water in tanks.
It should probably pay for itself inside three years.
It could be the small tank is no longer working and its having cold water in it ?
This might mean that if you use 4 gallons of warm to cold water from it, then there’s 4 gallons of hot water added to it. So then in a while there’s 2 gallons of hot water at the top, and the rest has mixed to warm up the rest of the tank. So you get to use it the 2 gallons of hot water, and then it returns to warm…
So do the temperature measurements thrice
When its been a while since hot water is used, go out and feel the inlet and outlet on the tanks
Run some hot water, go out to the tanks and feel the inlet and outlet pipes
When you are having a problem with shortage of hot water, go out and feel the pipes