Honeywell L4006A2114 Aquastat on Megastor IWH

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Old 03-11-12, 10:00 PM
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Honeywell L4006A2114 Aquastat on Megastor IWH

The aquastat doesn't turn the boiler on for about 7 minutes when there is demand for hot water. When the boiler does start, it sees really low return water temperature from the IWH. Since the boiler has been off, the return temp takes a few minutes to recover to 130+. The aquastat has no differential adjustment, although the information I have says that it's factory set a 5 degrees. It may be working fine, as it's located half way up the tank, and may not see alll of that cold water pouring in right away. I'd like to change the control, so that as soon as there is demand (the cold side of my mixing valve drops 60 degrees immediately which i can use to start boiler. I still need the aquastat to limit the max temp in the IWH, but need the boiler running earlier when there is demand. Ideas?
James
 
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Old 03-11-12, 10:15 PM
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Hello James,
Have you tried to simply turn up the temperature?

Are you indeed running out of hot water?

I'm not sure i understand what's going on with the mixing valve, sorry.

Peter
 
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Old 03-11-12, 10:40 PM
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Hi PeterNH,
Thanks for the reply. My description may be lacking.

I'm able to adjust the max temp of the water in the IWH using the aquastat, which I have set quite high, as I'm using a mixing valve on the output side of the IWH, bringing the ~160F water in the tank to a useable 120F at the faucet.

I'm not running out of hot water.

My problem is that the return water temp to the boiler drops below 130F and takes a while to recover when the boiler finally get the demand signal, which as I understand it is bad for a non-condensing boiler. I could use a mixing valve on the boiler return loop, or use the valves to force more through the bypass, but either will reduce the effectiveness of the IWH. I think, that if I can get the boiler to start sooner (as soon as cold water starts to replace the hot) I can keep the return loop above 130, which is better for the cast iron boiler, and will improve the responsiveness of the IWH. I'm looking for ideas on configuring the controls, or advice as to why this might be a bad idea.
 
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Old 03-12-12, 05:29 AM
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Hello James,
Ahh ok.
I've been having a similar debate in my mind.
My ihw return, typically takes from 2 to 3 1/2 minutes to go above 115, 115 is ok for oil.
You have gas, i think?
I have a tripple aqua stat and if the boiler temp, not the return, goes below about 115, then i have the ihw pump wired to shut off until the boiler temp goes over about 145. Takes about 2-3 minutes. If the boiler is alread hot, say over 160, the pump allways runs.
A typical frst firing for my ihw is 9-12 minutes.
Many folks tell us, that low return temps for 3-4 minutes are nothing to worry about, especially if the burner keeps running for a good while after, to dy things out.

Peter
 
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Old 03-12-12, 04:46 PM
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My problem is that the return water temp to the boiler drops below 130F and takes a while to recover when the boiler finally get the demand signal, which as I understand it is bad for a non-condensing boiler.
It's only bad if after the heat call ends, it's put up wet.

As long as it comes up to temp within a few minutes, AND runs long enough afterward to dry the flue passages out, there is no problem, as Peter has said.

What is/are the reason/s you are running the indirect at 160 ?
 
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Old 03-12-12, 10:55 PM
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Understood regarding getting the boiler to temp. It runs for at least several minutes at +140F before shutting down. I may stop losing sleep about that.

Regarding the higher WH temp, I'm using a net 50MBH boiler and a 34 gal IWH to power 3+ baths for 5 people. By upping the temp, I'm able to support back to back showers, or to fill the jacuzzi tub with one pour. The system's new, so I may be able to get by with lower temp, but given the "smallish" size selection, I wanted to make sure there was adequate hot water, and from the family's perspective it works great.

Here's a pic.
IMG_0032 | Flickr - Photo Sharing!
It's not perfect but neither am I.

I'm considering adding a switch to manually call for boiler heat, energizing the primary circulator and cycling the burner continuously, keeping the primary loop at about 180F. This would be Max Mode. When the WH aquastat calls for heat, the WH circulator comes on. This mode would provide the fastest response when unusually high demand is expected. In Normal Mode (switch off) the aquastat will control both the boiler (and primary pump) and the WH pump. The only downside I see is the wasted energy keeping the primary circuit hot.

Thanks for the solid responses.
 
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Old 03-13-12, 03:50 PM
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Regarding the higher WH temp,
Logical... try backing it down and try to find the lowest operating point where you still have adequate hot water. The lowest setting you can get away with is obviously going to be the most cost effective. I wouldn't go below 140... google 'Legionella' to learn why.

The circulator almost out of sight on the right side of the pic is installed improperly. See:

http://www.taco-hvac.com/uploads/Fil...ry/101-029.pdf

Not right away, but eventually, that circulator will become noisy and ultimately stop working. With the motor 'down', there is undue stress on the thrust bearings in the assembly. Fix it now, or fix it later, and when you do fix it later, rotate the flanges so the motor shaft is horizontal.
 
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Old 03-19-12, 11:27 PM
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Got it NJ. Great catch with the pump, I'll swap it for a rotated one, as there's no room to turn the flange with this strut (Which is goofy.)
Thanks for the help!
 
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Old 03-20-12, 03:40 PM
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Check the flange to flange dimensions on the rotated flange pump. As I recall it's different. Might need a 'pipe stretcher'.
 
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Old 03-21-12, 07:28 PM
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I have stated many times there is way too much emphasis on flue gas condensation in cast iron boilers. As trooper stated it is just important to get above 130f within a reasonable time and be dry when it shuts down. There is more problems encountered by too quick boiler recovery by over sized boilers than flue gas condensation.
I have worked on thousands of residential boilers and have seen very very few affected by flue gas condensation, although I cannot think of more than about a dozen, commercially I have more concerns.
 
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