Manual reset high limit

Does this not mean that the boiler will reach a max of degrees before shutting off? If so, then why are either of the reset high limits even being reached? With a setpoint of , which was too low, which I ran for several years, the limit temp was never reached for obvious reasons, but I am unable to grasp why it is being reached now.

I realize now that I have been referring to the offset in the recent posts, but saying "differential". Sorry for the mistake. The meaning of the offset or differential varies- there is no industry-wide standard definition. Sometimes it refers to how far below the setpoint the water temp has to be before it re-fires, sometimes it means how far above the setpoint it will run before turning off.

A safety high limit lockout normally can't be overridden by the other controls, even if the parameters of those controls allow programming it to a temperature higher than the safety. That may be what you're running into. The manual reset kit is probably somewhat generic across their product lineup, some of which may have a higher safety limit, but the safe operating limits of the WHN don't change when the kit is installed.

Try backing off the setpoint to F, with a 10F offset, or a F setpoint with a 5F offset and observe it's behavior. Bumping the boiler temp up doesn't help if there isn't enough burner. If you're not sure what your actual heat load is, run a fuel-use based heat load calculation to get a pretty close ball-park number. But you could also be radiation limited, in which case the boiler would always be able to hit it's setpoint temperatures without actually reaching full-fire.

A bit of napkin math would be able to show if that's the case. I calculated the radiation potential several years ago and don't recall that being an issue. Is there any reason not to drop the offset to 2 deg?

I just created another thread where I was basically asking how critical the offset setting on a mod-con is, since the unit decreases the firing rate before it hits the setpoint.

It just changes the firing rate to hover around the setpoint. The reason I ask about how critical the setpoint is is because I want to avoid short cycling. Perhaps I can decrease the offset setting and increase the differential to avoid this?

Opening up the temperature swings increases the minimum burn times at water temperatures when the radiation can't deliver the minimum-fire output of the boiler, thus reducing short-cycling. With high-mass high water volume radiation it usually doesn't matter especially at the fairly low minimum-fire output of the WHN but with fin-tube convectors it does. If the burn times are less than seconds the short cycling potential at condensing temperatures is high. I am not sure if my heat emitters are low mass.

They are just standard lengths of fin tube baseboard radiators. By doing this experiment at F, I am not quite sure what I am testing for. Seems like this would tell me how capable the boiler is at maintaining a tight range? Is there a reason I should try this at such a low temp of ? To get that type of efficiency out of it, the entering water at the boiler has to be under F, with an average water temp in the fin-tube of about F:.

Thank you, Dana. I have not yet done the test above as I am still not past the point of avoiding the high reset limit lockouts. I am unable to make any sense of this for the following reason: I have been incrementally decreasing the setpoint 1F at a time until I get to the point of avoiding the lockout.

I am now at F with a 1F offset! This makes no sense to me, as I can visibly watch the unit fluctuate firing rate to maintain within just a few degrees under the setpoint, or exactly at the setpoint, and it rarely goes above it. It does this until the space-heat demand is satisfied. The boiler pump and dhw pump are both programmed to run, I believe 20 seconds after the space-heat demand is satisfied. It's a bit like shooting in the dark without it. How does the system behave when you open up the offset to 10F or higher, with the temperature set to F?

I don't have any documentation on the manual reset kit. Was not aware of any. These controllers come in a variety of sizes and ranges for applications that utilize existing wells. This product is sold exclusively through our Professional Partners. Use the Find A Pro link below to locate one in your area. Published: PDF. Check with your company admin to get an invite to your company's profile, then create your own account. If your company does not have a Pro Portal yet, have your company admin sign up here.

Then you'll be able to select which homeowners see your logo based on the pricing per household consumer will not be charged. Skip to main content. Roll over image to zoom Right click on thumbnail to save image. Liquid Temperature Controllers for Every Application The Aquastat controllers from Resideo are immersion type devices for limiting or regulating the temperature of liquids in boilers, storage tanks, and other applications where temperature control is required.

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