Aquastat setting

gyrfalcon

Is this setting correct for 180deg water temp? This is how last company left it.

Alan (California Radiant) Forbes

It looks more like 190°.

bburd

High limit aquastats usually have a 10° differential. That one is set to cut out at approximately 190° F, and cut back in at 180° F.

pecmsg

For general use fine. 

This time of year it could be lower. 

gyrfalcon

So the metal prong is just for the high limit stop?

MikeAmann

YES.

Alan (California Radiant) Forbes

Isn't that the operating limit, not the high limit?

MikeAmann

L8148
Immersion-type controller that combines high limit protection with switching relay control of burner and circulator motors. High limit opens burner circuit only.

In this case, this unit only has 1 limit, which makes it the operating limit and/or the Hi limit. Whichever you decide to call it.

EdTheHeaterMan

Residential Boiler controls for single family home does not require separate operating limit and high limit controls. If the boiler is located in a public building the AHJ may require a second limit that is set higher than the operating limit. That second High limit may also need to have a manual reset.

The L8148 control that is pictured is currently set at 190° and has a non adjustable 10° differential. So that control will open the burner circuit (shut off the burner) when the water temperature at the probe reaches 190°. When the water temperature drops to 180° the burner circuit will close (Burner fire on) and the burner will fire as long as there is a call for heat from the thermostat or zone control connected to T T of that control.

gyrfalcon

So if the dial is moved clockwise so triangle arrow points to 180, it will lower the values to 180 high cut out and 170 low to turn boiler on. I don’t think the dial moves lower than the 180 number. 

Alan (California Radiant) Forbes

The spec's. say:

Operating Temperature Range (F): High Limit-- 180 F to 240 F

gyrfalcon

So to go any lower, I need a different aquastat.  It seems some favor electronic versions from Honeywell/ Resideo or maybe Hydrolevel.  

bburd

That is a high limit safety control to shut down the burner if the water in the system gets too hot. It is not supposed to be an operating control to maintain normal temperature in the system. Other controls should perform that function.

gyrfalcon

I’ve got my contractor scheduled to come out soon to service the old boiler.  It’s been mild and haven’t had to use it yet .   Thanks to everyone’s input / explanation on the function of the aquastat.

gyrfalcon

Boiler has a clean bill of health for this season. Heat exchanger is cleaned up along with inspection and exhaust gas combustion test .  Showing 78-80 % efficiency. 

STEVEusaPA

How can a combustion test show 78-80%?

gyrfalcon

Sorry for my ignorance in asking, but should I look into this further? Am I missing something? On a 40 yr old lp boiler rated at 82%, the 78-80 % seemed reasonable to me.  The tech was here while I was at work and this is what my wife reported to me. 

EdTheHeaterMan

STEVEusaPA said:

How can a combustion test show 78-80%?

Waiting for the stack thermometer to get to steady state and reading this chart can have some room for interpretation. Just one possibility, Steve.

But using the digital meters there should be an exact reading at a specific point in time. That is the number that should be given. Perhaps the LP Gas technician was just offering an opinion based on what he saw on his test equipment at a few different observations during the several minutes the probe was inserted, taking a reading. It appears that those numbers keep changing over the 5 to 10 minutes that the test is performed. That has been my experience anyway.

MikeAmann

I agree with what @EdTheHeaterMan said above.
Take my mother's boiler and HW heater for example.
The CA numbers seem to settle while the stack temp is around 420 degrees.
I try to record the numbers at that point for an apples-to-apples comparison.
But if I let the burner run for a couple more minutes, just before the limit turns the burner off, the water temp is 20 to 30 degrees higher and so is the stack temp. This brings the efficiency down slightly.