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Obviously one can’t start to heat when the other ones depleted since there’s no time for the recovery process. Sounds like two water heaters in tandem is not the right solution for large quantities of hot water.
Two tanks can most certainly provide double the hot water but they need to be set up properly. If the inlet/outlets are hooked up wrong OR one tank is not heating water when they are parallel OR the second tank is not heating water when in a aeries you'll have problems.
To me, and without knowing other specifics of your installation, a family of four should be able to get along just fine with a single 50 gallon gas water heater - not multiple heaters. Gas WH recovery is fast, certainly faster than an electric heater. It seems to be a waste to maintain stored hot water you don't need. Heating water to temperature (120 degrees F is standard) is known as recovery - that is how long to heat incoming water at ? (between 50-70 F) degrees to full temp that will satisfy the thermostat and shut off the burner.
I'm assuming these heaters are installed as mentioned above in series - that is cold water into the cold side of one tank, then that tank hot feeds into the cold inlet of the second, then that WH hot outlet feeds the house? Sound right? It is also possible they are installed in parallel.
Regardless, I'd agree it's time for a plumber to come evaluate what is going on. Could be any number of things.
To get a little more technical, and give you other things to consider, there's this:
The Federal standard for hot water outlet temperature has been 120 degrees F in residential applications for years. There is now evidence that as temperatures have been lowered by the government to meet safety standards (against burns/scalding dangers) hot water delivered at those lower temps could be causing "unintended consequences" of not being hot enough to kill bacteria in the water.
As a result, new WH's are likely to have 140 degree minimum (stored water) temperature settings on them PLUS the addition of a tempering valve (that mixes hot with cold water to achieve the desired outlet temperature back down to 120 F). With these changes, a benefit of the increased storage temp is a net increase in the total amount of available hot water at the desired outlet temperature into the system. It can get complicated to understand sometimes, so rather than giving you too much, I'll leave it there and let you discuss options with your plumber.
Question about the safety switch and other things, wouldn't that only affect one of the hot water heaters? Do they both have separate safety switches, thermostats, etc? If it were just one not working, then I would think I'd have hot water at first and then just run out. I apologize for my ignorance.
If you only have one tank working it's only when they are in a is series and it's second tank that is on that you'll get consistent hot water but that makes having two tanks pointless becsue you only have the capacity of the one tank.
To me, and without knowing other specifics of your installation, a family of four should be able to get along just fine with a single 50 gallon gas water heater - not multiple heaters.
Actually if you have one that can be set very high and utilize mixing valve one 40 gallon tank is sufficient. I have one like that and I tested it, easily had one hour for the shower and that wasn't some lukewarm shower with a water saving shower head either. Not sure what the internal temp was but probably in the high 150's if not low 160's.
You need to utilize mixing valve if you do this so someone doesn't get burned.
Actually if you have one that can be set very high and utilize mixing valve one 40 gallon tank is sufficient. I have one like that and I tested it, easily had one hour for the shower and that wasn't some lukewarm shower with a water saving shower head either. Not sure what the internal temp was but probably in the high 150's if not low 160's.
You need to utilize mixing valve if you do this so someone doesn't get burned.
Agree that a 40 gal may be adequate installed as you stated, but a 50 gallon @ 120F at the thermostat with no mixing valve. I believe WH's are coming set from the factory at 140 F w/tempering valves installed. That's why I recommended that the OP get a plumber in and discuss safe, appropriate options.
Probably a defective/worn out heating element in one or both units. Call a plumber in to check them out.
After 15-years, this is perhaps the most likely problem. You might want to consider a 'tankless' water heater. We've had great success with these! It seems like there is always an unlimited supply of hot water; if necessary (??), the heating element is easily accessible and you can save the space (and potential problems) of TWO water heaters.
After 15-years, this is perhaps the most likely problem. You might want to consider a 'tankless' water heater. We've had great success with these! It seems like there is always an unlimited supply of hot water; if necessary (??), the heating element is easily accessible and you can save the space (and potential problems) of TWO water heaters.
I totally agree and would think a tankless heater would be a better option than having two water heaters in tandem.
I’d be inclined to go with a tankless heater which would save energy, supply endless hot water and free up the footprint of two water heaters. Guessing they installed two since the 80 gallon units are now restricted to commercial use only due to energy code laws.
Thank you for all the responses. To clarify a few things:
The units are only about 4-5 years old.
This problem only started a few months ago. Until then, everything was great, so I'm assuming they were installed properly.
I'm not 100% sure exactly how they are installed, but it was explained to me that they use water from one heater, then the other one kicks in if the first runs out. This is pretty standard here from my understanding, and the way the builder installed it. When we had the units replaced, we didn't change anything about how the hot water worked, just replaced the old tanks because, well, they were old.
Temp is set at 120 and always has been. We haven't touched that since they were installed.
I'm not running out of hot water, it is just not hot from the get-go. It's maybe luke warm at best, even after the shower running for 20 minutes, it never gets hotter. This happened yesterday. I woke up, got in the shower, not hot. This morning I had a blissfully long, hot shower. No idea why. No one else in the house was even awake, and a shower's the first thing I do, so no other hot water had been used.
If I am correct in assuming that it uses one tank then switches to the other if needed, then my guess is that tank 1 is not heating at some times for whatever reason.
But it looks like I'll be calling a plumber. I'm just afraid that everything will be fine when he's here, making it hard to figure out. Because truth be told, it's fine most of the time.
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