Problems with Indirect Fired Hot Water Heater

catch22

So, a local heating company recommended a Weill McClain AquaPlus 45 and associated PEG 45 Boiler when our 30 year old system failed last year.    While they recommended this combination, watching the install work, I suspect it wasn't something they had done before (lots of swearing and complete redo of the piping on the second day).     

Anyway, I've noticed that the system is causing the house to run hot whenever there is a significant requirement for hot water.   I'm an engineer by background, and this doesn't seem right from a systems perspective.  I have to assume that the boiler is intended to run hot (but not make steam) for hot water demands.  A circulating pump pulls hot water from the boiler to the heat exchanger in the HW heater which should make plenty of hot water.   The specs on the HW heater also advertise very low temperature loss and very fast recovery, which is why we bought it.  

Has anyone else had experience with this sort of system and seen this type of operation?    If this is how it's "supposed" to work, I'm not sure we would've gone this route.   I suspect there is something wrong with either a pump or the wiring,  but it would be nice to hear from others before I call the installers back in.   




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Tom

I don't know if it's working right or wrong, and I haven't had a system like that, but cursing and puzzling are not signs that they're doing something out of their scope or expertise. Every installation can present its challenges, since each one is different. I think your questions are fair to the plumber, so ask them how it is supposed to behave.

Are you saying the house gets uncomfortably (or unnecessarily) hot? If it's not uncomfortable, are you concerned that you're consuming excess fuel needlessly?


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catch22


Tom_Reingold said:

Are you saying the house gets uncomfortably (or unnecessarily) hot? If it's not uncomfortable, are you concerned that you're consuming excess fuel needlessly?

Yes and yes.  With the household thermostat set to 67, the house routinely hits 69 or 70, and one can feel the radiators heating up and actually venting air (i.e. the system is producing steam).    Clearly, that is using more fuel than necessary.   



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Tom

Not necessarily. Cycling on and off takes energy, so it might be more efficient to overshoot the target than to hit it exactly and cycle off. That way, it cycles less frequently. Steam is complicated.


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Erik


Tom_Reingold said:

Not necessarily. Cycling on and off takes energy, so it might be more efficient to overshoot the target than to hit it exactly and cycle off. That way, it cycles less frequently. Steam is complicated.

Nope, that's not the issue.   If th.e thermostat is set to 65 and the temperature is already 66 or 67 due to solar heat gain or cooking for example, the thermostat isn't calling for heat.  It's the hot water heater doing it. I'm the go-to guy in the neighborhood for steam issues, and this has nothing to do with the normal single pipe steam issues u essex.


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Sir Dave

Control issue. Shouldn't be steaming unless house thermostat calls for steam. Indirect control (aquastat?) should stop the boiler @180-190 degrees.


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catch22


Sir_Dave said:

Control issue. Shouldn't be steaming unless house thermostat calls for steam. Indirect control (aquastat?) should stop the boiler @180-190 degrees.

That's what I was hoping to hear.      


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master_plvmber

There are two aquastats on this system. 

One is the immersed operating control on the indirect water heater which energizes the pump circuit and closes the burner circuit via an accessory double-pole double-throw relay.  
The other is an aquastat set in the block of the boiler which opens on temperature rise to break the burner circuit without manipulating the pump circuit.

Catch-22, you've been on this board a long time, you're an engineer and the "go-to guy in the neighborhood for steam issues". I'm surprised you didn't contract a more technical company to install your equipment. 



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plungy

Is your system zoned with pumps or zone valves or is there just one heating zone?   If zoned with pumps did they install flow checks to keep the zones from unwanted circulation bleeding in from other zones?    Maybe post some pics?


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catch22

Sorry - late getting back to this.    The firm that installed the system came back and re-did some of the piping.   Looks like there were multiple issues, including the fact that the circulating pump (the one that pulls the heating water from the boiler to the HW heater) had failed.   So,  it was essentially a gravity-feed that was pulling the boiler water to the HW.   I'm less and less convinced that this was the right path to go down.   There are now several valves to prevent unwanted circulation and multiple sensors.    I'm guessing either a tankless HW heater or a good-old-fashioned "white tank" with a pilot light might have been simpler and less prone to failure.  


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catch22


master_plvmber said:

There are two aquastats on this system. 

One is the immersed operating control on the indirect water heater which energizes the pump circuit and closes the burner circuit via an accessory double-pole double-throw relay.  
The other is an aquastat set in the block of the boiler which opens on temperature rise to break the burner circuit without manipulating the pump circuit.

Catch-22, you've been on this board a long time, you're an engineer and the "go-to guy in the neighborhood for steam issues". I'm surprised you didn't contract a more technical company to install your equipment. 

I surprise myself sometimes.   We were under the gun when the old boiler failed mid-winter.   The firm that did this is a "household name" in Maplewood with a strong reputation for service.   To be fair, they've worked hard to get things working correctly.    But, reading the installer's guide for this unit,  there are a lot of potential gotchas in the piping.   By my count, there are at least 5 checkvalves required, 2 aquastats, and a circulating pump for the standard install.   That seems like a lot of potential points of failure.   

I'm curious if you are recommending these (as opposed to say traditional or tankless).   


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master_plvmber

I recommend and install them all year long. I know where you might see two check valves on a piping diagram but not 5. 


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plungy


catch22 said:

Sorry - late getting back to this.    The firm that installed the system came back and re-did some of the piping.   Looks like there were multiple issues, including the fact that the circulating pump (the one that pulls the heating water from the boiler to the HW heater) had failed.   So,  it was essentially a gravity-feed that was pulling the boiler water to the HW.   I'm less and less convinced that this was the right path to go down.   There are now several valves to prevent unwanted circulation and multiple sensors.    I'm guessing either a tankless HW heater or a good-old-fashioned "white tank" with a pilot light might have been simpler and less prone to failure.  

I disagree respectfully catch 22. There is no better way to supply hot water than an indirect water heater when installed properly IMO. The key is properly sized piping in and out of the coil and check valves on supply AND return lines.  I have one in my own home going on five years now and it performs spectacularly. We don't recommend them for steam systems however.


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catch22

Thanks MP and Plungy.    Spent some time tracing the piping today against the installation guides, and you were right - 2 check valves.   Guess I was just grumpy given the amount of fiddling that's been required to (finally) get this system working right.    Plungy, curious about the comment that you "don't recommend with steam."    



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master_plvmber


catch22 said:

Thanks MP and Plungy.   Plungy, curious about the comment that you "don't recommend with steam."    

So am I actually. 


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plungy

Steam is not a closed pressurized system and the water temps are hard to control. The water circulated through the coil would also be filthy and lead to problems with corrosion etc.  What I like about the indirect is that it is elegant in it's simplicity. No chimney, no fire of it's own or gas supply. The tankless heater has many controls, is dependent on water flow and there are limits as to where they can be installed. 


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catch22


plungy said:

Steam is not a closed pressurized system and the water temps are hard to control. The water circulated through the coil would also be filthy and lead to problems with corrosion etc.  What I like about the indirect is that it is elegant in it's simplicity. No chimney, no fire of it's own or gas supply. The tankless heater has many controls, is dependent on water flow and there are limits as to where they can be installed. 

So, interestingly, despite the latest rounds of piping updates, water temps at the tap (e.g. kitchen faucet) are still very variable.   Using a digital probe thermometer and a cup of continuously filling water (i.e. letting the water run into a big coffee cup while it spills over),   the hot is back up over 160F which puts it well up on the scalding hazard chart (0.5 second exposure to potential second degree burn).    Since it's been so cold the last week, the boiler is firing for steam every 10-15 minutes; seems to be making the situation worse.    

Regarding elegant simplicity...  I'm willing to debate that grin    There are now more valves, regulators, and pumps in this "system" than if I had a separate, standalone, old-fashioned Rheem system.  

Regarding the boiler water running through the heating coils,  I have to believe that any corrosion in there would be pretty catastrophic from a repair perspective.   I'm sure the coils would be pretty hard to remove/replace, no?    


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master_plvmber

Yes. An indirect water heater is more complex than a stand-alone gas-fired water heater tank. But it's better in nearly every conceivable way. We Gateway Plumbing people don't ever install indirect water heaters without mixing (tempering) valves on the outlet of the tank. It's the law in New York and other large cities for just the reason you're experiencing. I think your installer hasn't got much experience with indirects. Care to post a picture? I'm interested to know what's going on there. We install them all the time and never hear a word from the users again about hot water. 


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plungy


master_plvmber said:

Yes. An indirect water heater is more complex than a stand-alone gas-fired water heater tank. But it's better in nearly every conceivable way. We Gateway Plumbing people don't ever install indirect water heaters without mixing (tempering) valves on the outlet of the tank. It's the law in New York and other large cities for just the reason you're experiencing. I think your installer hasn't got much experience with indirects. Care to post a picture? I'm interested to know what's going on there. We install them all the time and never hear a word from the users again about hot water. 

Same here MP. For a while we were installing Weil Mclain which had balky thermostats but since switching to other brands have had zero complaints.


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catch22

Attaching photos of the installation.   Hard to get it all in one frame given the amount of piping involved.  


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master_plvmber

Oh my. That's all...my goodness.
You have to cut that all out and 1. use the right pipe size; 2. use the right pump; 3. connect to the right supply tapping in the boiler; 4. use a proper weighted flow check valve; 5. get rid of that tee on the supply/domestic water line/whatever that is...
That's a mess, catch22. It's got to be redone.


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justsaying

don't see it in the photo but you should have an automatic temperature mixing valve set to 120 deg to mix in cold water to the hot water supply when required to regulate the temperature.  this will eliminate every having 160 deg water 


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