Short cycling boiler. I'm stumped.

JMWHVAC

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.

109A_5

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.

hot_rod

https://forum.heatinghelp.com/discussion/comment/1829651#Comment_1829651

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.

ColdMainer

https://forum.heatinghelp.com/discussion/comment/1830449#Comment_1830449

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.

109A_5

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.

LRCCBJ

@109A_5

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:

1. Turn the thermostat all the way down to the minimum possible temperature. The house must be above this temperature for the test to work.
2. Turn the High limit up to 210.
3. Turn the Low limit up to 170.
4. Turn the "Diff" to 20.
5. 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.

EdTheHeaterMan

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 .

ColdMainer

https://forum.heatinghelp.com/discussion/comment/1830694#Comment_1830694

https://forum.heatinghelp.com/discussion/comment/1830688#Comment_1830688

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" ?

LRCCBJ

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

LRCCBJ

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.

ColdMainer

You guys are wizards.

EdTheHeaterMan

https://forum.heatinghelp.com/discussion/comment/1830820#Comment_1830820

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.

LRCCBJ

That's the perfect sketch, Ed. Thanks for putting that up. It will really help him.