Ask Me Help Desk - Dual hot water tanks

One of my customers has a problem which has me baffled. He has two gas fired, 40 gallon hot water tanks, connected in series (6 years old). They are turned up just one 'click' from the highest setting. Normally when a tank is turned up this high the water is boiling hot, but in this case it was just comfortable. When I left a couple of hot water taps running the hot water seemed to run out quite quickly (considering its two forty gallon tanks)

I am unsure which path to follow for the repair. Part of me is saying that it's the thermostat on the primary tank which isn't working, therefore pumping colder water in the secondary tank. Also, I'm thinking it could be the dip tube on the primary tank? The tanks are 6 years old so the dip tubes shouldn't have decomposed.

Any suggestions?

Thanks in advance:)

Went back there tonight and checked the temp at the drains with my digital thermometer (I tried this on the tank in my home first so I could compare readings) Readings were good. I then checked the dip tubes which were also fine. There was definitely heat loss between leaving the secondary tank and arriving at the faucets, but the basement was immaculately finished so I couldn't investigate any further.

I increased the temperature on the secondary tank a little bit higher. Even though both tanks are set quite high, I figure that the secondary one doesn't fire as often, so increasing it should give an extra few degrees. Perhaps a 50 gallon tank further down the line might be in order.

Thanks for the tips folks, I can now troubleshoot a basic tank blinfolded, now I just have to figure out the power vented beasties... whole other nightmare! I'm sure I'll be on and off here quite a bit, and I'll try and rattle the odd tip jar along the way.

I would check the easiest and most likely first and that is to check out the dip tubes on both water heaters.

Psst! How hot is the water coming out of the drain? Especially just after the burner turns off.

Quote:

Originally Posted by letmetellu

I would check the easiest and most likely first and that is to check out the dip tubes on both water heaters.

I disagree! Replacing a thermostat's much easier then removing the cold water inlet and checking the dip tube. If replacing the stats doesn't get it then tear into the heaters and check the dip tubes. Just my opinion. Regards, Tom

In trying to diagnose the problem of not having enough hot water you have a choice of how you go about it, first you can change the thermostat on one of the heaters, if this does not solve the problem you can change the thermostat on the other water heater, if this does not eliminate the problem you have been out the cost of two water heater thermostats and still have the same problem. Or you could change the dip tubes in both water heaters, one at a time and if this doesn't solve your problem you will have been out the price of two dip tubes which would be far less than two thermostats. But you might still have the same problem. But the choice is yours.

Quote:

Originally Posted by KeepItSimpleStupid

Psst! How hot is the water coming out of the drain? Especially just after the burner turns off.

Definitely check this first. If the water out of the drain on the first water heater is hot, hot, hot, and the water out of the drain on the second(in line) waterheater is cool or cold, then you most likely have a problem with eh second water heater. This would cause the first water heater to heat both tanks(which is impossible, unless you have a recirc pump on the system.)

This is just my opinion, but if the second water heater were working correctly, you would get at least 30 gal of hot water, but if the second water heater was not working, the first hot water heater would pass its hot water through 40 gallons of cold water)

The first thing you need to do on a series pipes system, is make sure that both water heaters are functioning correctly. All things must be checked. Burners light, dip tubes are in good shape. I would agree with the thermostat replacement, but only on an electric water heater. You said you have gas, which means you would have to change out the entire gas valve(as the thermostat is a built in probe on the gas vavle that goes into the tank to sense temp).

Let us know if both units are firing. And remember, if second tank(in series) is working, you will get a significant amount of hot water. If second tank is not working, you may not get hot water for some time.

Both heaters fired up pretty much as expected. The primary first, followed by the secondary a while later. Now that you mention it, there was a bit of a delay (couple of minutes) before the water got hot.

I'm going to check and change the dip tubes first, as mentioned changing the gas valves will be pretty expensive on gas heaters. If it isn't the dip tubes I may just have to recommend changing the heaters... parts and labour for 2 gas valves doesn't make any sense on 6 year old tanks.

The temperature was set pretty high on both tanks, thus making them cycle 'on' more often. Combine this with the fact that Calgary has hard water... Is it possible that there may be so much scale built up inside that it could seriously affect its performance?

Open the drain. Test the water temperature.

Do what KISS suggets, if you get great hot water here but your water at the taps cools quickly then its likely the dip tubes. If the water from the tank drain is just warm you need to get new stats.

Quote:

Originally Posted by leetaylor

Both heaters fired up pretty much as expected. The primary first, followed by the secondary a while later. Now that you mention it, there was a bit of a delay (couple of minutes) before the water got hot.

I'm going to check and change the dip tubes first, as mentioned changing the gas valves will be pretty expensive on gas heaters. If it isn't the dip tubes I may just have to recommend changing the heaters...parts and labour for 2 gas valves doesn't make any sense on 6 year old tanks.

The temperature was set pretty high on both tanks, thus making them cycle 'on' more often. Combine this with the fact that Calgary has hard water...Is it possible that there may be so much scale built up inside that it could seriously affect its performance?

After you have replaced the dip tubes here is a suggestion that you might try if you are the type that would do the work yourself. Thermostats on water heaters very seldom cause problems, and if they do it is a over heating protector built onto the thermostat that once it turns off from being too hot it is then ruined and will not work again. So you might want to try what I have written below.

Before you buy two new heaters go to a plumbing wholesaler and ask if he would let you rob a couple of the thermostats off a leaking heater or a heater that they have had to warranty for some reason, very often they have one that is just two or three years old. Install them on your heaters and see if they solve your problem.

Just out of curiosity, is there a circulating pump on the system?

If there is, does it have the proper number of check valves on each side of the pump?

If it doesn't have check valves or one of the check valves have malfunctioned, then you might have cold water forcing itself past the pump and into the hot system.

Just a thought.

Iamgrowler asked you good question. I have seen return on hot water circulation pump connected in wrong location - into outgoing hot water line. Check it out...

There was no evidence of a circulator pump. I have yet to see one of those on a basic water system in Canada.

It's a bit of a mystery really. The house is only six years old, so its not as if Joe Blow handyman messed up the water lines over the years. They still have hot water, its just not quite as hot as it should be.