Peerless Boiler / Riello F5 - Short Cycling?

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  #1  
Old 01-21-21, 08:03 AM
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Peerless Boiler / Riello F5 - Short Cycling?

Good morning,

Boiler is behaving oddly - when the thermostat calls for heat, the system starts the circulator, turns the burner on and heats up to the target temp. Hi/Lo is set to 180/160. Per temp gauge, boiler heats up to 171 (always been that way), circulator keeps running but the burner shuts off. After a few mins, the internal temp drops to around 165 which turns the burner back on and it runs for a few mins, bring temp back up to 171 or so and shuts off again until circulator drops the internal temp to around 165.

I don't recall the system behaving this way - the burner would always stay on while the circulator was running. Where should I start? Radiators are all hot, I checked a few vents upstairs and none had air and each convector was hot as well as the water that squirted out from each vent when depressed.

Is the circulator not pumping enough water through? It's a Grundfos variable circulator and the system behaves same way regardless of the circulator being set to Med or Hi speed.

thanks.
 
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Old 01-21-21, 11:45 AM
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Try increasing the 'Hi' to about 190* watch the temps & see if that increases the burner run time. What is the number on the boiler control?
 
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Old 01-22-21, 08:05 AM
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Will try, thanks Grady.
Does that shorten the lifespan of the unit, having higher HI limit?
 
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Old 01-22-21, 09:57 AM
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No, it does not shorten the lifespan. The short cycling is far more detrimental.
 
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Old 01-24-21, 08:22 AM
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So I increased the Lo and Hi by 10 degrees but same symptoms present only at a higher temp. It takes about 2 mins to bring the internal temp up by 10 degrees while the circulator is running.

Not enough heat being carried away? What would affect that?
 
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Old 01-24-21, 10:50 AM
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Hi -

Should the LOW have been increased for the test? Maybe that should have been left where it was. See what the experts say.
 
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Old 01-24-21, 10:51 AM
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Dampers on the convectors open fully? Fins clean? Thermostat set the same? Have you tighten up the house via windows, doors, or insulation? Grasping at straws here obviously.

Zoesdad & I were replying at the same time. Yes, the low should have been left alone. Only adjust one or the other. Hi up OR Lo down.
 
  #8  
Old 01-24-21, 11:57 AM
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G,
You should have your hi/lo temps at least 20 deg. apart which you do.Since you have a hi/lo setting I'm guessing you have a tankless coil. The 20 deg seperation is to stop the boiler from short cycling which yours is doing. If you have 160/180 your boiler should be shutting off at 180 if the stat is still calling but the pump should continue to run until the stat is satisfied. If calling for hot water only it will shut off at 160 and with a 10 deg dif would come back on at 150.

What is the brand and model aquastat you have and what is the dif set at. It sounds to me like your problem may be in the aquastat sensing bulb.

Z had a suggestion of leaving your LO at 160 to see what happens. That sounds like it would be worth trying to see how the boiler reacts.

Pics of your aquastat with the cover off would be helpful if possible along with the model info. to get a better idea of what you have.
 
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Old 01-25-21, 07:24 AM
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Here are the photos,hope they're accessible, Honeywell 8124A controller.
I have a 40 gallon indirect water heater acting as zone 2 - the issue i'm seeing is during home heating cycle when t-stat is calling for heat.

"If you have 160/180 your boiler should be shutting off at 180 if the stat is still calling but the pump should continue to run until the stat is satisfied. " - this the exact behavior i'm seeing - the boiler shuts off and kicks back on after temp drops around 6-10 degrees below max.
 
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Old 01-25-21, 08:27 AM
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I had the same exact symptoms with an 8124A. The water temp would drop to 170, the burner would come on, temp hit 180 and burner would turn off, temp drops again to 170, burner comes on and so on.

Turned out the circulator was not coming ON which would explain the observations. Are you sure your circulator is coming ON?
 
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Old 01-25-21, 08:30 AM
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Yes, the house is heating so that's not the issue. Convectors are hot and clean - the only difference is that the temp hits the high limit and boiler turns off. Prior to recently, heat was being carried away more efficiently? The boiler wouldn't hit the high limit with circulator running and would only turn off once the t-stat wasn't calling for heat.
 
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Old 01-25-21, 08:44 AM
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Oh yep - You did in fact say that. My bad. Once in a while my system hits the high limit and the burner shuts OFF. I donít know when or why. As you say, itís like your efficiency took a drop. I wonder if it would have something to do with a drop in your circulator efficiency. I think you have a more complex circulator than mine. Wonder if the variable speed isnít working correctly. Wild guess!

Hope the experts can solve this.
 
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Old 01-25-21, 09:18 AM
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One thing I should've mentioned - I did replace my nozzle as part of annual maintenance around 3 months ago from .85, 60W to .75, 60B. I was only able to find this one in the store but haven't see any changes in heating or performance until last week.

Could that have anything to do with it? Would a solid code heat up the boiler core faster hence causing high limit shut off?
 
  #14  
Old 01-25-21, 11:16 AM
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G, -

This came from the link below. Sounds like according to that, changing the gallons rate a little and changing to a solid cone would be OK, but I have heard varying opinions about whether the people there know what they are talking about.

The folks here do (doesnít include me Ė lol). I think they will weigh in.

You can substitute an oil burner nozzle SIZE that's a bit larger or smaller - that's the gallons-per-hour number, or for your two examples 0.75 gph is the same on both nozzles.Ö

You can sometimes also substitute a different specialty nozzle, like changing out a hollow-core flame (HC) for a solid core flame (SC)
https://inspectapedia.com/heat/Oil-B...tion-Guide.php
 
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Old 01-25-21, 11:54 AM
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The decrease in nozzle size should make the burner run longer.
 
  #16  
Old 01-25-21, 03:30 PM
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G,
On your aquastat you have a black knob marked differential. It is set at 20. Set it to 10 and your results should vary. Without getting into it what it does is changes the temp ranges of the boiler.

Hope this helps a little.
 
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  #17  
Old 01-25-21, 03:35 PM
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G,
On your aquastat you have a black knob marked differential. It is set at 20. Set it to 10 and your results should vary. Without getting into it what it does is changes the temp ranges of the boiler.


Z,
As far as your question about the burner shutting down at certain temps it sound like you have a tankless coil and your LO limit is set at 160. With your differential set at 10 it is running the way it should. Your pump only runs on a call for heat, the rest of the time the boiler maintains temp for domestic hot water. I f your LO is set at 160, your HI should be at least 180.

Hope this helps a little.
 
  #18  
Old 01-26-21, 08:21 AM
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S,-

Yep I have the coil just as you surmised and the settings are as you outlined. So looks like all is well.

thanks!!!
 
 

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