My indirect hot water tank is overheating due to the way it was plumbed, looking for advice.

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Jod5908

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My hot water circuit from the boiler that heats my indirect domestic hot water heater has flow through it any time one of the heating zones has flow regardless of whether it's separate circulation pump is running, causing my domestic hot water to heat to 180F and has now ruined the relief valve on top.
Just bought the house and didn't think much of the hot water from the tap being scalding hot... Until my wife told me there was water and steam coming from the boiler. Upon investigation the water heater relief on top of the indirect water heater tank was continuously lifting. Figured at first it was the thermostat, but operation of the switch, control signal to the boiler and the power to the circulation pump all checked out fine. So I unwired the circulation pump and dialed the thermostat on the water tank all the way down and I was still getting flow through the heating loop to the domestic water heater. Turns out whoever installed the system (god knows how long ago, as I just bought the house a month ago), used a swing check valve on the outlet of the circulation pump in the heating loop. Also, the water coming from the water tank goes through the circulating pump, the swing check valve and connects to the main return only a couple inches from the suction of the main circulating pump for the 3 heating zones. Now I know a flow-check valve should have been used to prevent gravity syphoning of the hot water from the heating loops through the hot water heater when demand is not wanted. The water going to the domestic heater taps off my 1st floor (largest) heating loop downstream of it's flow-check valve. But when I turn off the 1st floor heating loop and turn on the 2nd floor heating loop, it is still drawing significant water through my hot water heater (heating the water inside to 180F) even when the hot water tank circulating pump is off/unwired.

Here are some pictures of what I am talking about.

https://imgur.com/StPYTfM
https://imgur.com/f4gHXOc
https://imgur.com/jQcWJvn
https://imgur.com/cxPvodJ

So my concern is that even if I replace the swing-check valve with a flow-check valve, that due to the way the indirect water tank loop for is piped, the heating zone circulator is going to draw a suction on the discharge of the water heater loop and still draw water through it. Which is overheating my water heater and diverting flow from my heating loops making my system very inefficient.

My other thought was to for-go the check valve altogether and put in a 110/120VAC Normally Closed solenoid valve. I would wire it in parallel to the circulator pump from the boiler so that when the water tank thermostat tells the boiler to kick on the circulator, the solenoid valve will also open allowing flow through the loop. When the water reaches the desired temperature and the 120VAC signal is cut from the pump, it would also be cut from the valve and the valve would close, preventing unwanted flow through the water tank.

While I'm fairly certain my system should have been piped very differently, is this a legitimate fix for the problem?

Thanks,

John
 

John Gayewski

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Yeah a zone valve would probably be a decent fix. I hate the way this is set up and would personally redo it all. But I realize that's not something most people would do.
 

Jod5908

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So, I've decided I'm going to rip out the swing-check and install a Taco flow control valve. I'll just wire it up to the IWH thermostatic switch and the thermostat terminals of my R485a. That will solve my unwanted flow issues and overheating of the IWH. I understand that there's a lot of issues with the rest of the plumbing. It bothers me that there are no isolation valves for the three separate heating zones besides the flow controls and having the heating circulator directly on the main return to the boiler is probably not the best. The boiler is about 20 years old and I plan upgrading the system in a couple years so when I do that, I also plan on reconfiguring the plumbing. Thanks for the feedback.
 
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