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Author Topic: No hot water to the heat exchanger  (Read 232 times)

MarkP

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No hot water to the heat exchanger
« on: November 16, 2020, 06:49:01 AM »

I just fired my boiler this year.  I only use it to heat my garage.  It is a homebuilt furnace, 180 gallons, and I'm heating a 1000 sq. ft. garage with a 10 foot ceiling.   It takes 2.5 cords a year. I fired it up yesterday, and it's not circulating.  I use a Taco 007, and even tried a spare pump.  The water drops 3.5 feet from the pump, over 8 feet to the garage, back up 2 feet, and then is plumbed to a floor level 18" X 20" heat exchanger. I re-plumbed everything in the garage last week, and flushed the heat exchanger, so all the lines were empty.   I have the supply going in the bottom of the heat exchanger.  I think I may have been better taking it in the top.

My first thought was airlock.  Not sure that the 007 has the power to push the air out of the heat exchanger, and back to the boiler.  Anybody have this issue or any suggestions?
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RSI

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Re: No hot water to the heat exchanger
« Reply #1 on: November 16, 2020, 07:56:27 PM »

Where is the pump located? Are you sure it is spinning? Are there any check valves anywhere is the system or inside the pump?
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MarkP

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Re: No hot water to the heat exchanger
« Reply #2 on: November 17, 2020, 04:20:53 AM »

The pump is hanging on the back of the boiler, and draws off the top of the firebox.  Yes, it's spinning, but it seems it can barely move the water.  I flushed the heat exchanger, and replaced all the lines in the garage.  I installed a bleeder valve in the garage, and when I open the bleeder, I get water, but doesn't move much.  I'm going to try to find a Taco 011 today.  I'll update as anything changes.

THANKS...
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Homemade OWB  (Smokey)
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One good woman that can cut and split wood
Le Roy, WV

RSI

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Re: No hot water to the heat exchanger
« Reply #3 on: November 17, 2020, 07:33:02 AM »

The 007 should be moving water. Are you sure it isn't mounted backwards?
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MarkP

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Re: No hot water to the heat exchanger
« Reply #4 on: November 17, 2020, 11:42:21 AM »

Yep... I've checked it all, and I've installed many of the Taco 007 pumps.  I know the arrow on the cast housing points to the direction of flow.  I know the pump is running.  I've used these pumps for the garage, and a 75' run to the house.  Never had an issue.  I'm overlooking something.   

I changed to a new Taco 011 an hour ago, The boiler is on 180 degrees.  It's heating now, but still doesn't seem to keep up.  I got quite a bit of air out of the heat exchanger.  The heat exchanger cools down fast.  I flushed it before I filled the stove, and it looked bad, but it appeared to be clear when I reinstalled it.  I have the supply going into the top, and the line in is hot, but it only runs a few minutes and the bottom is cool.  I've heated my garage for about 15 years with this set up... never an issue, and no real changes, other than re-plumbed the lines inside the garage, and flushed the heat exchanger.   My thoughts are going to the heat exchanger having a blockage. 

I've seen diagrams with the supply going in the top, and some in the bottom.  Is there a preferred method? It sits vertical.   Any really sure way to clean it?  I flushed with water, and I've used vinegar. 

Your thoughts?? 
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Homemade OWB  (Smokey)
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RSI

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Re: No hot water to the heat exchanger
« Reply #5 on: November 17, 2020, 07:56:02 PM »

If the water flows the opposite way that the air does then you get more BTU output. If the water goes in the bottom and out the top, it usually purges the air better.

It sounds like your heat exchanger or something in the line is plugged. Is there any way you can disconnect both lines and connect to domestic water line to try flushing it out?
« Last Edit: November 18, 2020, 09:47:55 PM by RSI »
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E Yoder

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Re: No hot water to the heat exchanger
« Reply #6 on: November 18, 2020, 02:28:16 AM »

 I was thinking the same thing, maybe some blockage reducing the flow so low it can't pick up air and push it out of the coils. I'd put a hose bib in the loop and purge both ways.
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MarkP

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Re: No hot water to the heat exchanger
« Reply #7 on: November 18, 2020, 08:56:24 AM »

I appreciate everyone's help and advice.  I've built 3 of these in the past 15 years, and never had an issue until now.  The other 2 are still operating today.

I just came in from the garage.  I have sharkbites on the heat exchanger, so it was easy to take out. I drained it, and I can blow through it easily.  BUT... I didn't get much water out of it or the lines.  Not what I expected to find.  I called a friend that's a Central Boiler dealer, and he said the hot water has to go in the bottom, but he didn't know if that is enough to cause an airlock problem. I'm going to flush it again, and reassemble.  I have a bleeder valve on the return line, where it exits the garage, which is the same height as the top of the heat exchanger.  I like the idea of purging both lines.  Domestic water should have enough pressure to force the air out.   

I just now turned the water on at each valve at the stove, one at a time, and had immediate flow through the lines, where they hook onto the heat exchanger.  No blockages there.  It's coming down to an airlock.  Back to the purging with domestic water idea. 

I'll let ya know how it goes.  And again... THANKS!! :bash:
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One good woman that can cut and split wood
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MarkP

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Re: No hot water to the heat exchanger
« Reply #8 on: November 18, 2020, 04:49:56 PM »

AND I HAVE HEAT!!!

It was air locked!!   I unhooked the heat exchanger, and flushed it with muriatic acid.  I hooked it all back up, with the supply going to the bottom.  I installed ball valves near the heat exchanger, in case I have to drain it again, and maybe I won't have such a mess next time. I did put in valves on the supply and the return, as it exits the garage, and put a hose big on the supply side, for just in case.  As I started the pump, I opened the supply side at the stove, but left the return closed, and opened the return valve in the garage.  Once all the air was out, I opened the return on the stove.  I had heat within a few minutes.  Big relief, and I appreciate E Yoder, and RSI for the advice.  I am quite mechanical, and I just finished building a Pro Street 1953 Chevy, but I just got beat by an air bubble....... lol 
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Homemade OWB  (Smokey)
Stihl 290, 2 Stihl 170s
Tractor supply 22 ton splitter
One good woman that can cut and split wood
Le Roy, WV

E Yoder

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Re: No hot water to the heat exchanger
« Reply #9 on: November 19, 2020, 03:19:54 AM »

Air is a funny thing, I've learned to "power purge" by the school of hard knocks.  :)
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MarkP

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Re: No hot water to the heat exchanger
« Reply #10 on: November 19, 2020, 05:30:37 AM »

I should have known to purge the air, as it's a common problem on most cars cooling system.  Live and learn!!

Thanks again!!
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Homemade OWB  (Smokey)
Stihl 290, 2 Stihl 170s
Tractor supply 22 ton splitter
One good woman that can cut and split wood
Le Roy, WV