Short cycling boiler. I'm stumped.
Comments
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I don't like power vents but sometimes you need them. When using power vent with a fairly short pipe between boiler and vent, I often use a butterfly damper (or other restriction) under power vent but above draft regulator. With that I can adjust a much greater static pressure in the unit and also slow down the hemmorhage of warm air out the draft regulator. I have seen units that had a hard time getting enough static to pull the static pressure switch because it has a free supply of air thru the draft regulator just a couple feet away.
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Hello ColdMainer,
If you truly think it is a circuit board issue or the prover switch relay, it may be just the solder joints where the relay is soldered to the circuit board, easy repair if you can. Probably not too hard to remove the board to inspect them. A change in temperature and vibration can often agitate a failing solder joint.
A meter would have helped the verify the correct functionality of the pressure switch and other system electrical attributes. Jumping wires and terminals and moving wires with systems that are timed can be awkward and lead to confusing results.
National - U.S. Gas Boiler 45+ Years Old
Steam 300 SQ. FT. - EDR 347
One Pipe System1 -
a great explanation by Ed. I would not think that all expansion tanks lose 1 psi per year? If so many boilers would be popping relief valves 5 years down the road. I can’t remember ever checking my expansion tanks over the years? You will need to isolate and relive any pressure to check it get an expansion tank valve with the bleed off port, if you plan on a yearly check.
Your system is steel and copper as far as I can tell, no open seal circulators so not many, if any places for O2 ingress?
After a short period of time the O2 in the H2O that you filled with is consumed in the oxidation process so you have mainly nitrogen left. Nitrogen is used in tires because it doesn’t migrate out as quickly as air, same in your expansion tank now.
Rumors abound that expansion tanks are pre-charged with nitrogen, so if that were true the charge will stay for a long time, nitrogen on both sides of the butyl rubber
My Amtrol connections have never confirmed the Nitrogen charge, but they do use use refrigerated air, which pull the moisture out, to lessen the rust potential on the air side
I would suggest the Extrol Pro tank, it is a plastic lined tank, stainless nipple.
Sizing is important also, from the looks of your system a #30 is adequate.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
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Good info. I just might try taking the CB out and looking it over.
I'm actually in my living room right now, I can hear when the powervent comes on and the flame from the burner when it starts. It just came on, so I started counting to 5, which is how long it runs in-between short cycling. But it kept burning. So I went down to see why. It looks like the temp dipped to 160 triggering the low setting on the aquastat, it ran to 170 and stopped. Powervent kept running like it should for post purge.
Not sure why it didn't short cycle, though. From what I gather, either I first start up the boiler from 0 degrees (like if I tried running heat all night and it shuts down) it runs nice all the way to 190 degrees where the high is set on the aquastat, but if there's a call for hot water or heat, though , that's when it starts short cycling. Just my latest observation.
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Also the relay solder joints to the circuit board in Honeywell aquastats is a known issue. The Red arrow points to the Relay. It as a much more awkward job to inspect the relay solder joints in the aquastat, much disassembly. Mechanical pressure (with an insulated nonmetallic tool) from different angles to the circuit board and the frame of the relay may identify a failing solder joint during a failed call for heat.
If the DHW call works consistently and just the call for heat is intermittent I would suspect the aquastat since the electrical path through it is different for the different operations. The Red highlight components is a thermostat call path which uses the relay the get power at B1 to B2, the DHW low limit path uses the contact highlighted Blue. If the solder connections are intermittent at K1 or 1K1 the power to the rest of the system will be intermittent too and only during a thermostat call. With a meter it would make short work of where the electrical path ends when the system acts up.
National - U.S. Gas Boiler 45+ Years Old
Steam 300 SQ. FT. - EDR 347
One Pipe System1 -
If the DHW call works consistently and just the call for heat is intermittent I would suspect the aquastat since the electrical path through it is different for the different operations.
Well stated. I agree.
This theory can be tested as follows:
- Turn the thermostat all the way down to the minimum possible temperature. The house must be above this temperature for the test to work.
- Turn the High limit up to 210.
- Turn the Low limit up to 170.
- Turn the "Diff" to 20.
- Disconnect the circulator leads and power the circulator independently from a standard outlet (not from the L8124). The circulator will run continuously.
Observe the behavior of the boiler. See if it will rise to 170F…………fall back to 150F……….and rise to 170F again without short cycling.
Of course you cannot leave it in this condition or it will overheat the building. But, it tests the L8124 to see if its K1 relay is problematical.
ALSO: When you get finished, move the THE DIFF to 15. This will cut the cycling of the boiler dramatically. Leave the LL at 170. Move the High Limit to 190.
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This is a great test @LRCCBJ. I had a feeling that the L8124 aquastat might be the problem before I realized that there was a Power Venter in the mix. I just remember that Field and Tjernlund power venters often break the Orange wire (burner motor) from the primary control and the change in pressure from the burner operation may trip the prover switch and cause a similar short cycling as a result of the open Orange wire circuit. This same function can happen if there is a fault in the power to the B1 on the L8124 that corrects itself after the relay looses power. Sort of like a buzzer or bell circuit b u t i n r e a l l y s l o w m o t i o n .
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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Okay I'll be home in a few hours so I'll check this out soon.
Could you please give me an idea of how to "power the circulators from a standard outlet" ?
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With the power off, open the cover on the side of the circulator. There will be two wires with wire nuts on them. Undo the wire nuts and connect the leads from the circulator (not from the incoming wire) to a new cord that has a standard outlet plug on it. You'll probably need to make this cord from an extension cord. Plug this into a standard duplex outlet. Now, the circulator runs continuously, independent of the L8124
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Ed,
In the second drawing…………..there is a path to the circulator……………when the K2 relay closes……………which is why I have him rewire the circulator………… I'm sure you already know this.
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You guys are wizards.
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This will eliminate or confirm the L8124 as the cause of the short cycle. When the thermostat calls for the L8124 to operate the circulator then the burner also operates thru the 1k1 relay contact. By having the low limit operate to 170°F with a 20° diff then there will be no reason to call for heat from the thermostat while the circulator pump operates from a separate power source. This will get the heat up to the radiators. The burner will operate as if there was no call for heat and the radiators will get hot enough the heat the house.
If the circulator pump powered by the other power source is shorting out the other power source, then we will know that the circulator is causing the L8124 to short cycle the burner. If the circulator pump operates fine from the other power source and the burner operates without short cycling when there is no call for heat, then we have pinpointed the L8124 as the problem.
You have given @ColdMainer a great test to eliminate two problems and confirm one of them.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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That's the perfect sketch, Ed. Thanks for putting that up. It will really help him.
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On additional point and it's important:
You are only going to wire that electrical cord to the circulator that is closest to the boiler. Don't bother doing anything to the other circulator (furthest from the boiler). That circulator is run by a different relay…………not by the L8124.
Of course, you won't get any heat to the zone that is run by the far circulator. But, be sure the thermostat for that zone is also set as low as possible for this test.
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Update
I wanted to wait a week or so and have a better understanding before commenting further.
I had the extension cord picked out and was ready to test the L8124 but noticed short cycling actually stopped when calling for heat. I waited it out to see if it snapped out of it for good or if it was just in some sort of funk. I did move a lot of wires around back and forth etc while working on it all Christmas week. Messing around w the powervent etc. Changing out the PRV. Maybe the pressure switch worked its way out of it? Showers were hot. Heat worked. No short cycling. Nice. Job complete! ..Whatever i did.
UNTIL yesterday. I got home and saw the thermostat calling for heat but could hear the boiler was quiet. Wife said water was cold all day. I thought , oh boy, here we go.
I grabbed that extension cord and removed the female end and wired her up to the circ pump. Followed the instructions from above. The circ was running on its own so I proceeded to turn the burner on. (The boiler temperature was around 120 F.) The burner began short cycling first attempt. Confirming the aquastat is not the culprit. Which brought me back to that powervent cb / proving switch.
I wasn't playing around now. I had ordered a new pressure switch that came in a few days prior that I had actually planned on returning. I wired the new one in and held my breath.
The boiler fired up without any short cycling. That was a good start. Ran to 190 F. Then I turned my 1st floor heat on and went back down to the boiler. This was the bigger test. Burner came back on and ran for the entire process. Zone was screaming hot. I went up and took a shower. Nice and hot. Now its morning, the heat ran all night. That was a surprise. Showers are nice and hot. And for now, the short cycling is over with.
Conclusion : The old pressure switch was going bad. Randomly working and then not working. It makes sense. I'll be looking at the Tjernlund circuit board itself if short cycling comes back. I can't imagine it being the fan or any obstructions in the flu. The fan is clean and tight. No vibrations. Quiet. Anyway, I'll take the W for now.
Fingers crossed.
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Great job Anthony,
You ruled out the L8124 and hit a home run with the pressure switch!
Hopefully, no more issues with it!
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Don't forget about replacing the expansion tank………………….
Also, did you set the L8124 differential to 15? It will reduce the number of cycles when calling on the Low Limit (maintaining temperature). Depending on the condition of the coil, you may not like the result in the shower (too cold at times). If so, you can try 10 and see if that will work.
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I have a waterworks tank but haven't installed it yet. I probably should do that soon. Was hoping to throw on one of those ball valves w a drain hook up when I do the job. Which now that I think of it, would a ball valve work the way it's intended if it's put before the tank? With a check valve being right in front of it?
And yes, I set it the way you suggested. Feels nice!
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The ball valve will work as intended if you install it DIRECTLY above the tank between the tank and the Watts air eliminator above it.
Now……….to save on oil………and this is an experiment:
Reduce the high limit to 170 and reduce the Low Limit to 150. I don't believe this will work for you……….because the shower will be too cold. But, please consider it a test to save fuel. The success depends on the condition of the coil and the flow rate through the showerhead. If you have a great flow without restriction in the showerhead………..just ignore this advise………….you cannot save fuel!
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Wouldn't you put the valve between the air separator and the expansion tank, so you can just close the valve then change the tank. So in the future no draining the system to change the tank.
National - U.S. Gas Boiler 45+ Years Old
Steam 300 SQ. FT. - EDR 347
One Pipe System1 -
Exactly.
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Thanks! I think she's looking pretty good now. I set this new tank to as close to 15 psi as I could tell and threw it on.
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Well done.
You should now be good for awhile!!
How'd you make out with new settings for the L8124?
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Is that 15 dif to help save on oil? Yup I've got it still set that way and it's going good. Not cycling so much.
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Ok, now that you have everything fixed and you have completed the 3 week crash course on Hydronics, Oil Heat combustion, and Electrical controls, your last tuition payment is due.
Please remit your final payment to my Venmo by scanning the Venmo Code in the PM I sent you earlier today. Once your payment is in my account, Mrs. Weight will distribute it to all of the instructors.
@LRCCBJ, @109A_5, @JMWHVAC, @hot_rod, @EBEBRATT-Ed, @HVACNUT, And all the rest of the instructors are familiar, Helen will be distributing their share of the tuition payment. As I tell all the Heating Helpers on the conclusion of every crash course, You have to go to Helen Weight for your money.
I'm happy that you are up and running properly now.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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Yes, the 15 allows the boiler to drop 15°F below the low limit before it restarts. Preferred over the previous 5°F to limit cycling. When there is no heat call, the boiler will fall to 145°F before it restarts. This might be too low for a comfortable shower. I don't believe you have witnessed this yet because the boiler is typically above 160°F for the cold months. You may see it in April, however, when the heat calls are widely spaced. If it occurs, raise the high limit to 190°F and raise the low limit to 170°F. You will only need these settings for the warmer months.
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Okay, I will experiment when I get back. I did notice the PSI was still around 20 once the boiler started to heat up. Do you think my gage might just be inaccurate or maybe I should take the expansion tank off and put a little more pressure in it/retest it? Though, I was pretty meticulous the first time adding pressure and checking it each time.
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No need to do anything. When the tank is properly charged and working like new, the pressure will stay very close to the cold setting on a system with a small amount of water (baseboards). If you want to see the gauge move, just put the old tank (full of water) back on the system.😉
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This is maybe the best thread I've read!! On the edge of my seat the whole time. Don't want to wammy it but kinda sad it's over. Nice work everyone. Nice work @ColdMainer
Miss Hall's School service mechanic, greenhouse manager, teacher, dog walker and designated driver
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Or when the system is cooler just close the valve you now have, then fire the system up, but don't let the pressure go too high.
National - U.S. Gas Boiler 45+ Years Old
Steam 300 SQ. FT. - EDR 347
One Pipe System1
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