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

jod5908

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

EBEBRATT-Ed

A flow check may fix it.

A zone valve will fix it. Control on the indirect could open the zone valve. The end switch on the zone valve would pull in a two pole relay. 1 pols starts the indirect circulator and the other pole fires the boiler.

I would like to see how it's piped.

How about some pictures of the system?

Zman

There are several things that could have been piped differently (and better). If the DHW had been tied in below the main circ you would not have the ghosting. Both circs should be pumping away from the expansion tank as well.
The 120-volt zone valve is probably the easiest fix.

mattmia2

You could move the dh circulator to befor the tee where the dhw loop connects and put an ifc in the dhw circulator or add a flow check in the dhw loop.

Zman

mattmia2 said:

You could move the dh circulator to befor the tee where the dhw loop connects and put an ifc in the dhw circulator or add a flow check in the dhw loop.

He has a swing check, the main circ is pulling it open because of how it is oriented.

JohnNY

I don't see how this would "ruin" your IWH's relief valve which shouldn't activate until 210° and 150 PSI. I usually install tempering/mixing valves on my indirects and run them kind of hot anyway. I'm told the hotter water keeps the larger tanks free of things like Legionella.

Just for fun in the short term, if the rest of the system will allow for the cooler return water, you could try turning your aquastat down to 160-ish and see if that keeps your relief valve from blowing off.

mattmia2

Zman said:

mattmia2 said:

You could move the dh circulator to befor the tee where the dhw loop connects and put an ifc in the dhw circulator or add a flow check in the dhw loop.

He has a swing check, the main circ is pulling it open because of how it is oriented.

So it would work as is if it were not tied in such that the dhw is essentially another zone on the dh loop's circulator?

jod5908

EBEBRATT-Ed said:

A flow check may fix it.

A zone valve will fix it. Control on the indirect could open the zone valve. The end switch on the zone valve would pull in a two pole relay. 1 pols starts the indirect circulator and the other pole fires the boiler.

I would like to see how it's piped.

How about some pictures of the system?

jod5908

JohnNY said:

I don't see how this would "ruin" your IWH's relief valve which shouldn't activate until 210° and 150 PSI. I usually install tempering/mixing valves on my indirects and run them kind of hot anyway. I'm told the hotter water keeps the larger tanks free of things like Legionella.

Under normal circumstances it would lift at 210 and 150, but I can only imagine how long the hot water tank has basically been at 180 due to the constant flow of heating water through it. At some point in the past, probably before I bought the house a month ago, it lifted and now will randomly lift and fail to reseat and the pressure in the system is definitely not getting above 150 psig and temperature should not be above 180 as my boiler output is ~180. I think it has lifted enough that I do not feel confident that it is working properly and its a cheap and quick component to replace, so why not. The incoming cold water to the indirect is preheated slightly passing through the boiler before going into the tank.

John

pecmsg

The primary pulp is drawing water thru the indirect.
Ruined the relief valve i doubt, 210°F or 150PSIG rating.
A quick solution is lower the boiler water temperature. What's it set at now?

jod5908

Right now it's 180F, and I closed the inline ball isolation valve upstream of the dhm circulator and unwired the circulator. I could lower the temp to 160F on the boiler, but that's just putting a bandaid on it. I would still have flow diverted from the heating loops through the dhw, making my whole system a lot less efficient. I need to stop the flow through the dhw loop when the thermostat is not telling the boiler to heat it. Based on how close the outlet of the dhw loop is to the suction of the heating circulator, I'm fairly positive that even with a flow-check valve, it's still going to draw water through the dhw loop when any one of the zones turns on based on the testing/troubleshooting I did last night.

I'm fairly certain that the only way I can fix this, without changing the whole piping configuration is with some kind of solenoid valve that would be off the same circuit as the dhw circulator pump and stop flow completely through the loop when the pump was not running. Just not sure whether to use a 24VAC solenoid or a 120VAC solenoid. I could provide power/control to either based on the available outputs of my boiler control circuit.

John

jod5908

pecmsg said:

Ruined the relief valve i doubt, 210°F or 150PSIG rating.

I'm not exactly sure what it's lifting on. I wouldn't imagine it's lifting on 150 psig because you would hear that through the whole damned house. It has to be lifting on thermal but the boiler water is only 180F, so there's no way for the secondary side of the heat exchanger in the water tank to get hotter than the boiler water, unless the temp gage for my boiler is off. So it's very possible it is now lifting at a much lower pressure and/or temperature than it's rated for. Regardless, the cheap relief valves installed on those things are notorious for failing and/or failing to reseat, especially after repeated lifts. It's a cheap fix ($12 valve) and easy to replace, just to make sure it's going to operate properly.

EBEBRATT-Ed

@jod5908

Check back later and I will post a quickie wiring diagram

Zman

I don't see an expansion tank on the domestic side. My guess is that it is lifting on pressure.

MikeAmann

EBEBRATT-Ed

@jod5908

The attached will give you some idea what to do. Depending on how your burner is started you may need to alter the burner start stop circuit which may be line or low voltage. I can't tell from your picture

JohnNY

jod5908 said:

I'm fairly certain that the only way I can fix this, without changing the whole piping configuration is with some kind of solenoid valve...

Why don't you want to use a zone valve?

mattmia2

JohnNY said:

jod5908 said:

I'm fairly certain that the only way I can fix this, without changing the whole piping configuration is with some kind of solenoid valve...

Why don't you want to use a zone valve?

I think they do, they just don't know the terminology.

Side note, nothing good comes from these boilers that come with a circulator attached.

EBEBRATT-Ed

To be realistic, It's probably better to pull the main pump out and move it above the tee and rework the copper tubing.

Probably less $$$$ than adding relays and zone valves and all the wiring. Drain the boiler repipe fill and purge probably 3 hr job

BDR529

Got a few things going on. Think you should call the guy and be done with it

jod5908

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 I agree that 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 everyone's feedback.

EBEBRATT-Ed

@jod5908

hope that works out

rick in Alaska

Personally I don't think a flow control is going to work. The way it is piped now, the boiler pump is going to want to pull through the water tank and the pump, with or without a check valve. You need to re-pipe it so the water heater pump is below the boiler pump.
Rick

hot_rod

A 120v zone valve is probably the same $$ as a flow check, and it would solve the issue for now. I doubt the flow check will.

mattmia2

It sounds like zone valve , flow check, and solenoid are getting confused here.

If you want the non fixing the piping solution you need a zone valve and need to use the end switch. The valve takes some time to open and you dont want the circulator deadheading on the closed valve until then.

If the aquastat on the indirect is controlling 24vac you can use the aquastat to control the zone valve and connect the end switch to what the aquastat controls now.

jod5908

rick in Alaska said:

Personally I don't think a flow control is going to work.

I'm not using a flow-check. Going with a zone-control valve. It's either shut or open, so when there's no heat demand on the iwh, there will be no flow through the loop.

mattmia2 said:

If you want the non fixing the piping solution you need a zone valve and need to use the end switch. The valve takes some time to open and you dont want the circulator deadheading on the closed valve until then.

If the aquastat on the indirect is controlling 24vac you can use the aquastat to control the zone valve and connect the end switch to what the aquastat controls now.

Yeah, that's what I plan on doing. Running 24VAC from my transformer to one terminal of the thermostat, the other terminal of the thermostat will go to terminal 1 on the Taco, terminal 2 on the Taco back to the transformer. Then wire terminals 2 & 3 (end switch) on the Taco to the T terminals in my aquastat. That should turn the circulator on once the control valve is open.

It's funny, being a brand new home owner, 4 days ago I didn't know anything about boilers and heating systems, but I've worked and maintained equipment in the engineroom of nuclear powered submarines for over 20 years so with some help online, some electrical schematics, a pencil and paper and my Fluke I now know exactly how the control systems work, the heating zones and the various loads that the aquastat can be configured for. The only thing I'm still learning is the actual plumbing, but one of the mechanics that served on subs with me was also a plumber before he joined the Navy so he's gonna help/teach me how to sweat the pipes and fill/vent the system.

Thanks again for all the help and feedback.

John

mattmia2

I'd use a taco zone sentry series instead of their old style valves. watch the cv of the valve too, the indirect needs a lot of flow.

neilc

jod5908 said:

, , , but I've worked and maintained equipment in the engineroom of nuclear powered submarines for over 20 years so with some help online, some electrical schematics, a pencil and paper and my Fluke , , ,
John

I read this the 1st time as, nuclear engineer with help from the internet , , , #smiling_face

thankyou for your service