Condensing boiler getting too hot and short cycling
I have a Burnham Alta 150 heat only propane boiler that is consistently throwing an "H01" (anti-short cycle) error code that shuts down the boiler for 3 minutes, then restarts. This happens dozens of times per day. The specific error code is H01/1.0, which the manual says "While thermostat demand present, boiler has cycled off too quickly due to temperature and restart is delayed."
I have a two zone hydro-air system, and can reproduce the issue in this sequence: Both zones are calling for heat and the boiler supply temp is at a steady ~150 degrees. However, as soon as one zone turns off, the boiler temp shoots up to 170 degrees causing the burner to turn off. From there, the temp quickly drops down to 140 which triggers the H01 code. Is this consistent H01 error code causing any damage to my boiler? Curious if anyone knows what the issue could be and if there are any settings I can adjust.
Here is a video I took this morning reproducing the issue:
Alta 150 heat only documentation:
Comments
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You have flow issue with the unit that is calling. The flashing light on the e007 is an error code which is saying you are air bound. trying purging the hydroair coil. depending on the manufacturer you will have a high point air vent that can be a coil vent or a drawoff (hose connection)
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Thanks, @pedmec for noticing that. I think the flashing light was just due to my iPhone when taking video. For some reason when I take videos, it will appear as the lights are blinking for some odd reason! Anyway, I just took another look at the e007 and it's a solid yellow light throughout all zones.
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It's really hard to see in the video, but it sure appears to be piped wrong (no hydraulic separation) which would most definitely cause the issue you're seeing. Can you share some pictures of the piping from different angles, showing any closely spaced tees or hydraulic separator/ low loss header as required by Burnham?
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@GroundUp , thank you for the input. I just took some photos of the piping from various angles. Are these ok?
Also, the video I took prior showed a flashing light on the circulator, which was not actually true. My iPhone camera was making the light appear to flash even though it wasn't. The light is solid yellow when boiler is on, so safe to assume it's not air bound I think.
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You don't have a flow issue and you don't have any piping issues.
What you do have is the inability of the boiler to modulate fast enough to prevent a shutdown on limit. This is common on mod-cons………especially big ones. I suffered with the same problem for 1.5 years until the manufacturer addressed it.
What you can try with this mod-con (of which I have no experience) is to go into the "modulation menu" and look for "CH1 max modulation". It's probably at 100 right now. Reset it to 50. I am simply guessing on the 50 with the assumption that it will be sufficient to heat the building on the design day. You will know if the building cannot maintain temperature on the design day (would be about 0°F here in CT).
I'm fairly confident this will stop the boiler from shutting down on limit. The delay to restart is normal to prevent this cycling from becoming ridiculous in terms of number of cycles per hour.
This boiler has other parameters that can be adjusted to assist with this situation but try the easiest first as stated above.
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The no flow was based on the circulator flashing. obviously turned into a camera issue.
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Thank you for the clarification, I did not previously see the low loss header below the boiler. It appears to be a well designed and executed system, though as has been mentioned, it now sounds to be a response time issue more than anything. Slow closing valves or a buffer tank are typically the way around this issue, but it does sound like the boiler is a bit oversized as-is so you may be able to manipulate the firing rate as LRCCBJ mentioned or possibly turn the supply water temp down to keep the firing rate lower.
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@LRCCBJ i appreciate your feedback, thank you. I’ll give it a try today by turning down the max modulation rate from the default setting of 100% to 50% and test. I could also turn down the central heat setpoint by 10 degrees or so (i.e. 180 to 170), like @GroundUp mentioned but I’ll try to max modulation rate first.
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Lowering the setpoint will not accomplish your goal. When one zone shuts down, the boiler will just climb away from 170 and the same thing will happen. The boiler, with the current settings, cannot respond fast enough to cope with the instantaneous drop in load.
There are other parameters on that boiler that address this…………..it has quite a bit of capability.
We'll see if the 50% works.
All mod-cons shutdown if the SWT climbs…………typically 10°F………….above the setpoint. My opinion is that most installers and just about every homeowner consider this normal behavior……………..which is not correct.
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Lower water temp = lower firing rate. So yes, it would help. Nobody suggested that it would do the job on its own, it's merely an addition to your firing rate limit.
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A better question is where is the outdoor reset and why is this boiler running at 180°F in the first place?
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@LRCCBJ , I lowered CH1 max modulation rate down to 50% and I could instantly hear the boiler become much quieter. Thanks for this tip! However, the supply temp seemed to climb very slowly and never got above 135 degrees (which is fine for most days). I tested increasing the CH1 max modulating rate to 60% and that seems better. The boiler runs much smoother now (a little more efficient I guess) and doesn't have those sharp spikes in temps causing the boiler to shut down. Thank you!
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Well done.
The 50% was just the initial attempt.
What is the SWT at 60% after running at least 20 minutes? What is the setpoint?
When one zone closes, how high will the SWT go before the boiler can modulate down and stop the climb?
Can you maintain building temperature with the CH max at 60% on very cold days?
You'll need a few days…………maybe week(s)………..to obtain the complete picture.
Patience.
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@LRCCBJ , I only let it run for about 10 minutes to monitor the results. I'll report back in a few days to get a better sense of the numbers once I let the system run longer. However, I did notice that when one zone closed, the SWT climbed to about 160 and then slowly modulated down with no short cycle error codes.😀
As far as set points, I just took a look in the settings and the CH1 setpoint is 180 degrees and the CH1 min boiler water temp is 130 degrees. Both are the default values from U.S. Boiler. Would you recommend adjusting any of these numbers too?
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If the setpoint is 180°, the boiler would not shutdown on limit until it reached 190°. So, that problem is eliminated because, apparently, the boiler cannot reach 180° when running at 60%.
But, the fundamental problem here is why the boiler is not setup for outdoor reset? This device reduces the water temperature incrementally as the outdoor temperature climbs. The installer sets up the maximum and minimum SWT and the maximum and minimum outdoor temperatures. The boiler follows this straight line. When it's 40F outside, the boiler might have a SWT of 130° and when it is 0°F, the boiler might have a SWT of 160°F. These numbers are just examples. The specific building requires it's own values and that is iterative work by the installer (or, more typically, the homeowner).
Running the boiler at 180°F wastes a ton of fuel when you don't need it. The goal with the mod-con is to get its return water down to 130°F for most of the season.
All mod-cons have the capability of outdoor reset if the temperature sensor is installed on the outside of the building (away from sun).
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I remember my installer mentioning something fancy about how the Alta boiler calculates everything based on the load. It does't sound this Alta boiler needs an outdoor reset, unless you think having one might only help? From my light research, this guy explains why Alta doesn't use an outdoor reset:
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Alta doesn't utilize ODR, but IDR. So you have to play with the temps manually
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Interesting.
This magnificent logic for the boiler apparently doesn't use indoor reset in the way desired. With outdoor reset, the boiler follows a straight line depending on outdoor temperature. With this boiler, it doesn't know the outdoor temperature so, apparently, it starts somewhere between the set max and min temperatures and waits to see if that will satisfy the demand. If it won't, it steps up in a "boost function" until it satisfies the thermostat or reaches the max temperature set (you previous set to 160F) and the min temperature set (130F from the factory).
Effectively, it will operate only between 130° and 160°…………never more………never less.
When you were observing that it "couldn't make 150°", it was in it's modulating mode. It won't go to 150° until it runs for a specific time and then it steps up because the demand was not met. This is desirable.
So, time for more experiments.
Return the F03 setting to 150°F.
Set the 503 setting to 90°F.
Wait 24 hours and don't even look at the boiler. Let's see what it does. Record both the outdoor temperature and the thermostat setpoint.
For the maximum efficiency, you want to find the lowest possible settings that will still heat the house. Of course this is variable depending on the outdoor temperature. When it gets warmer, you will want to lower the F03 setting. If you get cold and the room stays below the 'stat setting, you'll need to raise the F03 slightly. You prefer to stay at 150° or less because the return water will be at 130°……….ideally………..and you'll condense, which is one-half the goal of a mod-con.
This design, without an outdoor sensor, requires the homeowner to constantly reset the boiler………….otherwise it will cycle on limit fairly frequently. The goal is to keep the boiler running indefinitely at a low modulation…………..just enough to heat the building…………..which can be done with outdoor reset…………..not with this boiler.
I do see the capability of using an outdoor sensor since it is mentioned in he operating instructions.
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