Navien 180E NG

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Csvt18

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Hey guys

Overnight I noticed my navien tankless/combi boiler pre cycle purging a lot. This morning I noticed it would reach space heating temp of 150, keep burning for a bit then go over cutting out at around 154f. It would then stay on in condensing mode for about 3 minutes then pre cycle purge again before burning to reach 150f again.

Is this short cycling? Should I up the set temp? I don’t have an outdoor reset I adjust myself based on how cold it is (32f) this morning.

Why is the boiler going over the set temp causing it to stop burning?
 

Csvt18

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How are you controlling house temp?

Nest thermostats. 3 zones. No issues with those they hit temp it’s calling for. Just the boiler over fires the heating set temp and has to “back off” and turn off burn. Then it’ll reignite like 3-4 minutes later after set temp drops again.
 

John Gayewski

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Without an outdoor reset to tell it to modulate I would think it'll just go to top temp and run until the thermostat shuts it off. Are you saying the thermostat is shutting it off or not?
 

Csvt18

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Without an outdoor reset to tell it to modulate I would think it'll just go to top temp and run until the thermostat shuts it off. Are you saying the thermostat is shutting it off or not?

I do not have a reset. I adjust temp on navien unit myself depending on outdoor temp. The thermostat does shut it off when it’s satisfied. The navien unit however is over firing reaching past set temp thus having to turn off burner then refire again repeating this cycle until thermostat is satisfied.
 

John Gayewski

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I do not have a reset. I adjust temp on navien unit myself depending on outdoor temp. The thermostat does shut it off when it’s satisfied. The navien unit however is over firing reaching past set temp thus having to turn off burner then refire again repeating this cycle until thermostat is satisfied.
So the thermostat isn't still calling when the boiler shuts off? Or it is calling for heat when the boiler shuts off?

In other words is the cycling your talking about happening before the thermostat is satisfied?
 

Csvt18

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So the thermostat isn't still calling when the boiler shuts off? Or it is calling for heat when the boiler shuts off?

In other words is the cycling your talking about happening before the thermostat is satisfied?
Yes. It’s happening before. Because the boiler itself goes past the set space heating temp and has to shut down burn because it did so. For example. It’s set at 155f. It goes to 159-160 and shuts off burn until it drops to 145ish then re ignites burn to get to set temp again. All while thermostat is still calling for heat. I can tell each pre burn purge it does to rid the built up exhaust. It does this maybe 4-5 times a call for heat.
 

Fitter30

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When installing the nests did u program it for hot water heat? If not want to be with a meter to check r to w on all three zones. All heating and cooling thermostats have a differential so they don't short cycle. Boilers not uncommon 15 - 20°f room stats 3°. R - W. 0 vac calling for heat. 24 vac not calling for heat.
 
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Csvt18

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When installing the nests did u program it for hot water heat? If not want to be with a meter to check r to w on all three zones. All heating and cooling thermostats have a differential so they don't short cycle. Boilers not uncommon 15 - 20°f room stats 3°. R - W. 0 vac calling for heat. 24 vac not calling for heat.

We did. We didn’t have this problem last winter. The navien would never overshoot the set temp. Just long steady burns.
 

Csvt18

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How do I get to the burner off and on parameters? Just saw someone increased their burner off parameter from 4 degrees to 15. In other words mines turning off burner when it’s 4 degrees over. I want to increase this so it’s not constantly shutting off burner and re igniting.
 

John Gayewski

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We did. We didn’t have this problem last winter. The navien would never overshoot the set temp. Just long steady burns.
Short cycling is a problem when it's not that cold. Your boiler should run non stop when it's really cold. Other than that it's got too much power and needs to be told to modulate.
 

Csvt18

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Short cycling is a problem when it's not that cold. Your boiler should run non stop when it's really cold. Other than that it's got too much power and needs to be told to modulate.

I found out how to access “burner off” parameter. I upped it to 12 over instead of 4. We’ll see if it over shoots the set temp now. If it does it has a margin of error of +12 degrees now.
 

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I found out how to access “burner off” parameter. I upped it to 12 over instead of 4. We’ll see if it over shoots the set temp now. If it does it has a margin of error of +12 degrees now.
I think I would get an outdoor reset. You'll get a nice heating curve, and over time (depending on your controls) you should be able to get plenty of efficiency out of it without thinking about it all of the time.
 

Csvt18

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I think I would get an outdoor reset. You'll get a nice heating curve, and over time (depending on your controls) you should be able to get plenty of efficiency out of it without thinking about it all of the time.
Let’s get back to the main question. Why is the boiler going over the set temp of the space heating mode? It’s a set temp for a reason. Am I not seeing something ?
 

Fitter30

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Look at settings H,Land M pages 59 -60
Installation operation manual.
Write down their settings when ever making changes take baby steps and give changes time.
H recycle time
L burner off
M burner on
Boiler wiring cn10 terminal strip
T/T what control are they connected to?
 
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Csvt18

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Look at settings H,Land M pages 59 -60
Installation operation manual.
Write down their settings when ever making changes take baby steps and give changes time.
H recycle time
L burner off
M burner on
Boiler wiring cn10 terminal strip
T/T what control are they connected to?

I changed L to 12 degrees over. Now it goes longer if it over shoots and keeps burner on. Doesn’t cycle burner on and off as much now but still overshoots. What’s recycle time?

M burner on is still set at factory default of 4 degrees below set temp.
 
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