Odd boiler behavior

[_big_]

I have a 20 year old Super Hot Saturn Series 270K BTU boiler. It provides heat for an indirect water tank and 6 radiant floor zones.

Its working fine and I've never had any trouble with it for 20 years.

Mostly out of curiosity, I have "instrumented" my heating system. I can see/record when zone valves open/close, when the boiler fires and also temperatures at several points of interest.

Turns out this boiler is just down the hallway from my home office. Sometimes I can hear the boiler fire from my office. One of the things I've noticed (and a reason why I installed the instrumentation) is the boiler seems to run for short periods.

A zone will open demanding heat. This will cool the primary loop and eventually the boiler will fire. Typically the boiler will fire for just a minute or two bringing the primary loop back to its high set point.

Here's the weird part. Not infrequently, the boiler will fire about 2 seconds?? And then there is a short delay, and will then fire for longer, maybe 2 minutes.

I don't really know how the boiler controller works, but here is my theory for this behavior. Boiler senses heat demand in the primary loop. It first lights the pilot, waits for a hot pilot indication and then fires the main burner. For some reason, (electrical noise caused by the main boiler?) it decides the pilot is not hot enough, turns off the main burner and waits for the pilot temperature sensor to indicate sufficient pilot temperature and then finally runs the main burner long enough to trip the high set point.

Since it ain't broke, I don't intend to fix it, but perhaps somebody with more in depth boiler knowledge can clue me in on this behavior.

Below is a record of firing the boiler main burner. When the last number is 1, the main boiler is firing. The main boiler fires for 2 seconds, then shuts off for about 7 seconds. On again for 72 seconds. Off for 9 seconds and on again for 86 seconds. I would think that hysteresis of the low/high set points and thermal mass of the primary loop would disallow this sort of behavior??

boiler 2023-03-22 11:17:33.907509 1
boiler 2023-03-22 11:17:35.913209 0
boiler 2023-03-22 11:17:42.932223 1
boiler 2023-03-22 11:18:54.196067 0
boiler 2023-03-22 11:19:03.216447 1
boiler 2023-03-22 11:20:29.526114 0

 

[John Gayewski]

What other things are happening when the boiler acts this way? You have one circulator for the zones (with zone valves) and a seperate circulator for the primary loop? Or is there an internal circulator for the primary loop? Is the circulator also kicking on and off?

 

[Sponsor]

 

[_big_]

There is exactly one circulator pump for everything. It turns on when a zone demands heat. In turn, the boiler may fire up the main burner if the primary loop falls below the set point.

I've noticed some "funny stuff"/noise with my zone monitoring hardware. I'm still observing. I have a theory that when the boiler main burner fires it drags down the 24VAC supply which injects noise into the boiler and it confuses itself???

 

[John Gayewski]

There is exactly one circulator pump for everything. It turns on when a zone demands heat. In turn, the boiler may fire up the main burner if the primary loop falls below the set point.

I've noticed some "funny stuff"/noise with my zone monitoring hardware. I'm still observing. I have a theory that when the boiler main burner fires it drags down the 24VAC supply which injects noise into the boiler and it confuses itself???

Hook up a meter and see if your theory holds.

 

[Fitter30]

Need the complete model number. The pilot igniter is it spark or glows red? Since you never had any problems has it ever been cleaned? Burners pulled and cleaned, top.of the boiler pulled and heat exchanger been cleaned?

 

[_big_]

Its 24 VAC. Noise difficult to catch with any sort of meter. I could connect a scope, but that's really hard to trigger for noise on AC.

I may connect the scope anyway on a slow sweep speed. Might show something.

I looked at the 24 VAC transformer. Its pretty small, but part of the boiler itself. Presumably Super Hot provisioned the proper size transformer. And there is a separate (quite large 24VAC transformer) for the zone thermostats.

 

[John Gayewski]

Its 24 VAC. Noise difficult to catch with any sort of meter. I could connect a scope, but that's really hard to trigger for noise on AC.

I may connect the scope anyway on a slow sweep speed. Might show something.

I looked at the 24 VAC transformer. Its pretty small, but part of the boiler itself. Presumably Super Hot provisioned the proper size transformer. And there is a separate (quite large 24VAC transformer) for the zone thermostats.

Why would it be difficult to catch? I think some alligator clips and some spare time would show you any variation.

 

[_big_]

Don't think a mechanical meter or sampling DVM would yield any useful info. An oscilloscope with a sweep rate set to show several cycles of the AC and long persistence should be able to catch a glitch in the AC.

 

[Fitter30]

Its not noise. Want complete model of boiler, the burner control brand and complete model and a pic of the wiring diagram. Without this info it's a non starter.

 

[JohnCT]

I could connect a scope, but that's really hard to trigger for noise on AC.

Any scope will trigger on 60hz AC - you don't have to trigger on the noise. You're just looking for excessive noise glitches or change in amplitude (of which there should be none) of the 24VAC, you don't need to analyze the noise specifically.

John