Boiler temperature? 125 is too low, right?

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Old 01-15-17, 12:02 AM
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Boiler temperature? 125 is too low, right?

- Single story, single zone hydronic heating
- Dunkirk boiler from 1992, located in basement
- Cast iron radiators all on first floor

I noticed on the boiler's dual thermometer/pressure gauge (needle style) that the boiler water temp is about 125. No other problems, thermostat set at 68 and house is at 68. Radiators nice and toasty as they always have been. Aquastat relay replaced 2 years ago.

The aquastat is set to 180. Does that mean it's supposed to keep the boiler at 180? And when a call is made for heat the circulator pump just turns on and the 180 is maintained?

From what I know about this boiler I could've sworn 125F is too low. Right?

I tried increasing the dial on the aquastat all the way up to 240 but nothing happens. Is it supposed to fire the boiler if you turn up the dial?

I'm confused.
 
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Old 01-15-17, 02:25 PM
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I suspect that you have a high volume system. Is this an older house, built in the earlier part of the last century? Does it have large pipes connecting the cast iron radiators?

If so then it may be completely normal to run at the lower temperatures. The burner is wired to only fire when the circulator pump is running and the room thermostat only controls the circulator. That means that when the thermostat "calls for heat" the circulator starts, the burner probably lights and the heated water is pumped through the radiators heating the house until the thermostat is satisfied at which time the circulator relay opens stopping the pump and the burner. This is a very economical method of heating the house as it does not heat the water any hotter than necessary and it also gives a much more even heat.

The one downside is that some boilers will have an "acid rain" problem in the combustion gas passages because they do not achieve a minimum exhaust temperature. This condensation can, under certain circumstances, be quite corrosive to the boiler metal and also to the chimney liner.

I would inspect the steel exhaust duct, the "smokestack" if you will, for thinning and corrosion. If there is none or it is minimal after 24 years of service I would say you have little to worry about.
 
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Old 01-15-17, 03:39 PM
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Before messing with any settings, I would verify the gauge. They are noted for inaccuracy.
 
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Old 01-15-17, 05:07 PM
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I suspect that you have a high volume system. Is this an older house, built in the earlier part of the last century? Does it have large pipes connecting the cast iron radiators?
Yes. Built in 1913. Cast iron radiators with large iron pipes suspended from basement ceiling. The last couple of feet connecting the pipes to the boiler have been updated to 1" copper. I installed a Spirovent Jr, an electronic LWCO, a new water inlet valve ("deleted" the pressure reducing valve and made it a true closed system), a new Honeywell L8148E aquastat relay, and a new 60# expansion tank last year, so it's somewhat updated.

If so then it may be completely normal to run at the lower temperatures. The burner is wired to only fire when the circulator pump is running and the room thermostat only controls the circulator. That means that when the thermostat "calls for heat" the circulator starts, the burner probably lights and the heated water is pumped through the radiators heating the house until the thermostat is satisfied at which time the circulator relay opens stopping the pump and the burner. This is a very economical method of heating the house as it does not heat the water any hotter than necessary and it also gives a much more even heat.

The one downside is that some boilers will have an "acid rain" problem in the combustion gas passages because they do not achieve a minimum exhaust temperature. This condensation can, under certain circumstances, be quite corrosive to the boiler metal and also to the chimney liner.

I would inspect the steel exhaust duct, the "smokestack" if you will, for thinning and corrosion. If there is none or it is minimal after 24 years of service I would say you have little to worry about.
That's good to know, thank you. The corrosion was the reason I was concerned. I'll take a look at the exhaust.

When we moved in to the house, the boiler was seeing 180F temps regularly. After all the repairs and upgrades were performed, I guess I don't recall the temperature dropping to 125-130 like it's at now.

What about the aquastat relay? Is it supposed to fire the boiler and raise the temperature when I adjust the inner rotary dial? It doesn't have any impact on the temperature, and to me, that says something's wrong. I'm no expert though.

Before messing with any settings, I would verify the gauge. They are noted for inaccuracy.
That was one of the first things I thought of. I checked the surrounding cast iron pipes closest to the boiler (the aquastat is mounted on one) with an IR temp gun and all of them are 125-130F, which I figure means the gauge is working correctly, right?
 
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Old 01-15-17, 07:10 PM
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Ir

The IR thermometer is not accurate on a pipe like this, and will undermeasure the temp. You need a contact thermometer. It is probably hotter than you are measuring.
 
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Old 01-15-17, 07:31 PM
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I do indeed have some corrosion. Not sure how bad it is. No holes or anything but it has that acid rain look to it. I vacuumed it up with a shop vac and it doesn't look too bad afterwards. Thoughts?

 
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Old 01-15-17, 07:54 PM
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The 8148 aquastat is a high limit aquastat. It will fire the boiler upon a call for heat unless the boiler temp is already at the limit. The burners will shut down upon either reaching high limit or the thermostat becoming satisfied.

That boiler with its relatively small volume & the large system volume you have, should have a by-pass.
 
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Old 01-15-17, 08:19 PM
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The 8148 aquastat is a high limit aquastat. It will fire the boiler upon a call for heat unless the boiler temp is already at the limit. The burners will shut down upon either reaching high limit or the thermostat becoming satisfied.

That boiler with its relatively small volume & the large system volume you have, should have a by-pass.
Interesting, makes sense though with the way it currently operates. Are you suggesting I swap over to a low-limit aquastat to maintain higher boiler temperatures?

Also, can you elaborate on the "bypass" and why you'd recommend one? I'm not familiar with that.
 
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Old 01-16-17, 11:16 AM
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If the boiler heats the house at 125, having it go higher would be energy wasteful. Have you ever watched the boiler temp thru a heating cycle? A boiler by-pass will reduce or eliminate the "acid rain".

Here's a thread from 2012 discussing a boiler by-pass. http://www.doityourself.com/forum/bo...ss-piping.html
 
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Old 01-16-17, 01:57 PM
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If the boiler heats the house at 125, having it go higher would be energy wasteful. Have you ever watched the boiler temp thru a heating cycle? A boiler by-pass will reduce or eliminate the "acid rain".
Yes, I have watched the boiler during a heating cycle. Never hits above 140. I will look into a bypass, thanks!
 
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