More (Boiler) short cycling

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Old 01-15-15, 03:02 PM
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More (Boiler) short cycling

OK, I'm putting the DHW issue on the side for a while. I notice in the morning when I turn a couple of the zones up from 67 to 71 or so, the boiler is cycling on and off maybe every 4 minutes or so until the room heat stabilizes at the higher temp. It might cycle like that for 5 or 6 cycles. Got the LL at 145, LL delta at 10 now and the HL at 180. What would I do to make the burn times last longer or is it not an issue? This new V8H boiler brings the boiler temp up much faster than the V14 did. Sometimes the burn cycle is only a minute or so, but not too much like that.

I'm having a hard time adjusting to the pre-burn blower run, when the V14 did that, something was wrong. I get the feeling this boiler is more efficient than the V14 even though it's rated even lower in BTU output.
 
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Old 01-15-15, 03:49 PM
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It might cycle like that for 5 or 6 cycles. Got the LL at 145, LL delta at 10 now and the HL at 180.
And what is the boiler temperature doing at this time?

I presume that the circulator pump is running all this time?

Without knowing the boiler temperature I can only surmise that what's happening is that the boiler is 'bouncing off the high limit'.

Boiler fires, pump runs, water up to 180 HL, burner shuts down, pump still runs, water in baseboards gives off heat and returns to boiler cooler, cools down boiler below high limit DIFF, burner fires, lather, rinse, repeat, until thermostat is satisified.

NORMAL operation during setback recovery.

What is your Hdf set to?

I believe default is 10F ?

So the burner will fire to 180, cool to 170, run to 180, etc.

Increase the Hdf to 20F and the burner will fire to 180, cool to 160, fire to 180, etc

This will give you longer burn times, longer off times.
 
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Old 01-15-15, 07:27 PM
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Your assumptions are correct. The circulator is mostly running all the time and it's bouncing between 180/170, while the zones are still calling for heat. But, "On Warm Start Boiler Control the High Limit Differential is not adjustable and is fixed at 10F."

I feel like I've created a monster. I don't remember if the V14 had Hdf, maybe it did. I think I still have the book, I'll look.
 
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Old 01-15-15, 08:12 PM
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"On Warm Start Boiler Control the High Limit Differential is not adjustable and is fixed at 10F."
Wonder why they would disable it?... weird.

I don't remember if the V14 had Hdf, maybe it did.
Guaranteed it did not.............
 
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Old 01-16-15, 05:24 AM
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Wonder why they would disable it?... weird.
Not that it's a big issue since I have the ODR, but I think the diff on my Vitorond 200 with Vitotronic 100 (KK5) controller is fixed as well. There is no knob for it (that I can see), only adjustments for the high and low.
 
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Old 01-16-15, 07:41 AM
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So the ODR adjusts the HL lower when it's warmer outside? I wonder If I would play with the HL, I could move it up and down depending on the outside temp. It would be a pain but do-able. Wonder if my V8H could be modded for the ODR? I may call Burnham and whine. But then they probably wouldn't recommend the ODR with a tankless coil. I may just have to live with it, I'm not buying another furnace.
 
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