Lochinvar Knight KBN150 boiler lockout

ARHL/HEX TEMP SW = Automatic Reset High Limit / Heat Exchanger Temperature Switch.

Some possibilites would include not enough flow from the circulator , air in the system, low water pressure, or bad sensor. When the boiler is operating see what the outlet water temperature is as determined by the display.

You might look into the programing. A pic of your sys would be helpful. Is your sys piped correctly? What type of boiler pump, fixed or variable? The boiler produces heat energy and that energy has to move into the distribution sys or else that heat energy stays in the boiler. You might want to look at the boiler pump delay in the programing or the ramp sequence. What type of fuel are you using Nat gas or Propane? Has a combustion anaylis been done?

Why did you think you needed a new blower? Was that the proposed solution to your current problem?

has the boiler ever been cleaned? The front removed and the chamber flushed out? There are way to force the boiler into high fire and observe the operation, watch boiler supply and return temperatures while on high fire or a DHW load.

Pull out the manual, I think that boiler control does some data logging to help solve intermittent faults and lockouts.

The water that has leaked out of the air vent inside the boiler looks pretty rusty, maybe flush the entire system, run a cleaner in it for a day or so.

I'd start with a good cleaning inside and fluid side and a combustion check after reassembling.

oops, I think this is the model you have?

https://www.lochinvaru.us/2018pages/kbn10.html

Perhaps flushing the system meant to wash the outside of the heat exchanger coils.

When I clean these, I first remove the back target wall. A small allen wrench probably metric.

Then maybe poke the target wall with toothpick or such and remove. You do not want the target insulation wall to get wet.

I use a pistol hose sprayer to rinse the coils. Also I use a credit card to cut the crud between the coils.

Even cut "saw teeth" into the credit card. You can feel and hear the "crunching" of removing blockage from between the coils.Saw and then rinse, the flush water should all go down the condensate drain line. Remember that all the gases of combustion have to pass thru the space between the coils.

The drain line should take a good flow from the hose. This also rinses the drain line all the way to the end. I then take the cond trap/neutralizer apart for cleaning. There is a float in it to shut down the boiler if trap is plugged.

While this much apart I clean the flame sensor rod and spark ignitor also, stainless steel wool or scotch brite pads.

Careful air gun cleaning of the burner itself.

Is that an indircet type water heater next to the boiler? If so it has a coil inside with boiler water, surrounded by the potable water to be heated.

The bottom of the separator should be piped like this so you can purge out debris.

You have the correct fittings, just in the wrong order.

You have fixed 3 speed pumps. If you flush the HX, you will flush the debris into the condensate neutralizer. Flushing the HX means that you take a hose with a nozzel and after cleaning the HX you squirt water thru the water tubes and flush out the debris that in the collection chamber under the HX thru the boiler condensate discharge tube. You would have to clean the drain trap if you didn't remove the drain hose from the trap when you flushed it. Cleaning the trap is part of the cleaning process.

I remove the hose and add another hose into a 5 gal bucket and then flush the HX. You would be surprised at the crap that comes out.

Mixing valves can lime scale inside theat prevents smooth operation, so they can stick or be slow to respond. They can be removed and descaled, rebuilt, or replaced if it is very old.

An example of a scaled valve, returned for warreanty as it would not regulate accuratly. On the right after descaling.