Hot water loss - Indirect water heater?

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Old 09-19-14, 11:00 AM
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Hot water loss - Indirect water heater?

I have a Burnham PV74wt oil fired boiler installed in 1998. My water is heated through a coil in the furnace. I have a large farmhouse with 2 zones. My main problem is that the hot water in my shower will be hot for a few minutes and gradually get cool for a few minutes. It then comes back hot and stays hot. I removed the mixing valve on the furnace temporarily and I don't have an "anti scald" valve on the shower faucet. This loss of hot water happens less frequently in the summer. It happens regularly in the winter. The boiler I replaced in 1998 had the same setup, but never lost heat. My parents have the same type of setup and never run out of hot water.

I have had at least one service person out every year for the last 15 years or so and no one has an answer. The best explanation I got is that my loop is too big and I need to add another zone. That does not explain it happening in the summer. It is serviced yearly.

I think I need an indirect water heater. Does this sound reasonable? I am 100% comfortable adding a standard electric water heater myself, but I have never installed an indirect. Is it a difficult job and do you have any recommendations? Or, am I completely off track. Thanks for any ideas.
 
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Old 09-19-14, 03:29 PM
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Is it a difficult job and do you have any recommendations? Or, am I completely off track.
Not real difficult... we'll talk about that later, let's do some sanity checks first before we talk about that.


What aquastat control is installed on the boiler, and what are the settings on the dials inside?


You say you have "2 zones" and by this you mean that there are two thermostats, correct?

If so, do you have ONE pump and 2 electric zone valves?

OR, do you have TWO pumps and no electric zone valves?
 
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Old 09-19-14, 07:21 PM
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Ok, sanity is hard to keep when the wife and kids are complaining about cold water The aquastat is a Honeywell electric aquastat L7224/L7248. My old adjustable one was replaced 4 years ago. It is currently flashing 170 and what appears to be 63. I have two thermostats. One upstairs and one downstairs. I have two taco circulator pumps and no electric zone valves. Thanks for replying!
 
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Old 09-19-14, 07:45 PM
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Is it possible that the " 63 " is really " bt " ?

If so, that's indicating that the boiler temperature is at 170.

Do you know how to access the various setting readouts? What I'm interested in finding out is what the LOW and HIGH settings are currently at, and what the DIFF associated with those is.

When they installed the aquastat, did they leave you with the instruction sheet?
 
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Old 09-20-14, 06:35 AM
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It could be bt because it looks like 63 but is missing a line on the 3. I preferred the old aquastat because I could adjust the temps and the time it took to turn on. They set this one and I have no idea how to adjust it. I had tried several different settings on the old aquastat and nothing made a difference. The service company thought the new one might help, but there was no difference.
 
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Old 09-20-14, 07:17 AM
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So they set it up and just left and didn't give you the instruction sheet... nice of them.

Let's start by you reading the instructions for the aquastat and letting us know the settings:

This one is called the "Quick Reference Guide" and tells how to view and set the a'stat:

https://www.forwardthinking.honeywel...-1957_2012.pdf

This one covers everything:

https://customer.honeywell.com/resou...0s/68-0281.pdf

You might want to download and print to keep with the boiler.
 
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Old 09-20-14, 07:50 AM
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While you are accessing the instructions and gathering the current settings, we can talk about the basic problem.

"Thankless" coils for domestic hot water use are a ridiculous waste of energy. Think about the energy required to maintain the boiler at say 140-150F year round, 24/7, just for the luxury of drawing a few gallons of hot water.

These coils are the most expensive way of producing domestic hot water, and the only worse way of doing so is a kettle on a wood burning stove. These things should have gone out around the same time as the horse drawn buggy, or when they invented sliced bread.

I removed the mixing valve on the furnace temporarily
This may in fact be 'counter productive'. This will force MORE flow through the coil and the water won't have as much time to absorb the heat from the boiler.

Perhaps there was a problem with the mixing valve to start with...

How exactly did you 'remove' it? Cut pipes and spliced?

One of the ideas behind the mixing is that the flow through the coil is slowed, the water in the coil comes out hotter, and is mixed down to correct temperature by adding some cold to it.

If your old valve was not of the 'thermostatic' variety, that was also part of the problem.

My advice here would be to replace the mixing valve with a good quality thermostatic one. It WILL help the situation.

These coils get 'limed up' (mineral scale) on the inside and this reduces the heat transfer. The mineral deposits come from the calcium, magnesium, and other minerals in the water. They deposit on the inside of the pipe over time.

There aren't many who still know how to do it, but it is possible to isolate the coil in the boiler and pump an acid solution through it for several hours which dissolves the scale and restores the coil to relatively new efficiency. It will still 5uck in the long run though.

The best explanation I got is that my loop is too big and I need to add another zone.
No, that's complete doo doo.

A sure fire (though expensive) solution would be to add an indirect heater. The boiler will be converted to 'cold start' and only fire up when the tanks thermostat tells it to.

If you are now burning oil (not sure what fuel you use?), believe it or not, an electric water heater won't cost that much more than the oil you might now be using. If you are burning natgas, the electric will probably cost more to run.

A separate gas fired water heater is another option if you have gas available. There are high efficiency direct vented models available if you don't have a chimney to vent into.
 
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Old 09-20-14, 01:14 PM
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Thanks for the links. I'll read through them later today. As for the mixing valve I just cut it out and sweated on a splice. What you said about removing the valve makes sense. I really did not think about it making the problem worse. My only concern about removing it is that I have to watch the kids extra close so they don't turn on the hot water. I do have hard water so I don't doubt there is scale in it. I have oil at 3.50 per gallon. Should I even bother trying to fix the coil and replace the mixer. My electricity is cheap, would an electric heater work as well as one fired from the boiler? In winter it is running all the time so it seems more efficient to use that heat for the water.. I'm not sure which way to go.
 
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Old 09-21-14, 10:17 AM
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Ok I read the online manual and understand the aquastat better. The high is set at 170 and the low is set at 150. High and low diff is set at 10.
 
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Old 09-21-14, 11:26 AM
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Let's start by increasing the DIFF on both the LOW and the HIGH.

Go up to 20F and see if there's any improvement.

The control may not allow a 20 diff on both with them set only 20 apart, so be aware that if it doesn't allow setting them both to 20 you can increase the HIGH side to 180.

Ultimately, I believe that you should actually DROP the LOW to 140 with a 20 diff, but see how just changing the diff goes first.
 
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Old 09-21-14, 12:02 PM
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OK made the changes. Since it is still warm outside and it is not heating the house it might take some time to see if that makes a difference. I still don't know what is best long term for heat and efficiency. I can reinstall the mixing valve and clean the coil. I did it several years ago with my father. We put I believe muratic acid through the coil. Or, I could disable it though the boiler and install a standard or heat pump heater. If I use the heat pump heater I could shut down the boiler in the summer and use the heat it radiates in the winter. Still not sure
 
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Old 09-22-14, 12:05 PM
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Hmm - it happened last evening. I always turn the hot on full blast and then add cold. The water did not seem quite as hot as usual and in less than a minute I had the cold water turned off and the water that came out of the hot was warm. After a minute or two I had to turn the cold back on because it got hot again. At least it did not get cold, and stayed sort of warm so that is a big improvement!

High is currently set at 180 low 150 and high and low diff are both 20. I have not reinstalled the mixing valve yet.
 
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Old 09-22-14, 12:35 PM
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You need at least 160 as a low. 10 dif. If you aren't getting hot water why would you turn the temp down? I always set lows to 160 or 170. Sometimes changing the guts isn't enough. You'll need to replace the body too. Most are easy enough to unsweat. If the pipe going into the hot side of the mixing valve is hot but it's cold coming out of the mix then you'll need to change the valve.
OK I just read the older posts. Put the mixing valve back in! When the boiler is running for heat you are going to have 180 degree maybe even up to 200 degrees coming out of the faucet. Get the Honeywell mixing valve. It's a better valve than the watts 70a.
So without the mixing valve you still have lukewarm water your tankless is most likely plugged. It will need to be replaced. I'm not sure that that is a diy project.
 
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