Parallel Water Heater Problem

[a716]

Recently I purchased a new house. The previous owner had installed two 40 gallon water heaters and hooked them in parallel. The two tanks are identical in make/model except one is brand new and one is 4 years old. Here is my problem, despite the piping appearing to be identical to both tanks, one tank is doing the vast majority of the work. The new tank is probably supplying 80-90% of the hot water and I can't determine why. Obviously this undermines the purpose of having the two tanks. Is there a way I can fix this? Here are some ideas I have had.

1) Could I minimize the water flow from the newer tank by regulating the hot water outlet with a valve and hope that this starts to draw more water from the older tank? As in partially close the valve. (this may be a stupid idea but maybe not?)
2) Remove the parallel setup and install the heaters in series. This is less desirable but if I can't equalize the flow I will have to

If anyone knows how to deal with this do let me know. Thanks

 

[SolagPlumber]

How many bathrooms are fed from these heaters?

 

[Mr_David]

Can you post a picture?

check the nipple coming in/out of older heater. Could be heat trap nipples.
They used to use a type that had a floating ball in the cold and a heavy one in the hot. this can reduce the flow just enough to cause an imbalance.
newer version are just a thin neoprene sheet with slits in them set down inside the tank fittings before the nipple are screwed in

 

[a716]

How many bathrooms are fed from these heaters?

There are only 2.5 bathrooms that these heaters are feeding. The one shower is a large walk-in with 6 heads. To be honest I have no idea why the previous owner felt the need to hook up two in parallel, not sure why there needs to be that much flow. But since the setup is there I figured I will keep it.

 

[a716]

Can you post a picture?

check the nipple coming in/out of older heater. Could be heat trap nipples.
They used to use a type that had a floating ball in the cold and a heavy one in the hot. this can reduce the flow just enough to cause an imbalance.
newer version are just a thin neoprene sheet with slits in them set down inside the tank fittings before the nipple are screwed in

I will try checking the out on the tank that is flowing less. How long ago did they use that type?

The only other difference is that the new tank is connected with sharkbites on the cold and hot and the older tank is connected with copper.

I do not have a picture on me at the moment, can get one later. But in the meantime here is exactly what the setup looks like.