Lochinvar Knight KBN150 boiler lockout

sunil314

Hello-

We moved into our house a few months ago and have had boiler problems. After our boiler shut down, a plumber replaced the blower (at significant cost). Since then, we periodically (every 3-5 days) get the following error and it ceases to work for hours at a time.

LOCKOUT

ARHL/HEX TEMP SW

I have raised the max temperature to the limit and lowered the setpoint (from 175→165) based on other posts, but it is not stopping this error/loss of service. Before I have another plumber come (with the relevant expense) I thought I would inquire on this board, as past posts have been helpful. I can not find what this error actually means on any web search or through either of the manuals for my unit.

Logistically my Knight boiler is connected to an indirect water tank for our running water, and also provides heat to our home through 3 HVAC zones.

Thank you in advance everyone!

TomS

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.

sunil314

the output water temperature is the same as the input (approx 68 degrees) and the rise is 0 as the system is not firing. We believe this shut off occurred when we turn on our laundry machine, although we run it several times a day usually without issue.

I notice on the parts list there is the water sensor and there is the automatic shutoff sensor. Should I replace the latter?

sunil314

When the fan runs, it's getting up to approximately 5000rpm

sunil314

how would I flush out air in the system please?

the last few times this has occurred it has self resolved after a few hours. This outage has been over 12 hours now

HomerJSmith

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?

sunil314

It is a natural gas system. It was professionally setup (the house was renovated but the boiler wasn't replaced). I don't know if the boiler pump is fixed or variable, I will post photos if it helps answer the question (sorry i'm the naive homeowner). The pump delays are all set at 30 seconds. The ramp delay is set to off. I have not done a combustion analysis (not qualified)

The new blower was the recommendation given to me by the plumber who came to fix the system. The ARHL HEX/TWS shutdowns have been happening periodically since he came in. We've been living in the house for 6 months without any issues prior to this. Thank you again for all the help.

hot_rod

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.

sunil314

I've watched a couple of youtube videos on HEX chamber cleaning. It doesn't seem complicated, could I do that myself? My ability to get a plumber here on a weekend is difficult, and all the part suppliers are also closed it seems so I couldn't even replace the HLC2510 if it was the trouble. Having no hot water or heat for the weekend with two young kids is not ideal.

sunil314

I put it into service mode (using the pin hole above the T) and it is now slowly showing a rise in the output. So the heating function itself seems to work.

hot_rod

excellent training at Lochinvar U. It does take some specific tools to check and adjust the burner. Cleaning is fairly easy, but you may want to have a gasket kit before you do any disassembly. The gaskets around the flame probes tend to break when you remove the rod for cleaning.

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

hot_rod

oops, I think this is the model you have?

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

hot_rod

This is a good product to have on hand when you open that boiler. Based on its age it may be due for some deep cleaning of the HX coils

44105BF1-1103-4221-AAB4-375201895D2A.png

3CA46141-FB24-46DF-9BE0-5269EF0BC5A0.jpeg

sunil314

Here's

a video of what happens when I restart the boiler

sunil314

i cleaned out the heat exchanger. It wasn't that bad inside. Someone suggested flushing the system. I don't see how to do that on the university website or in the manual

JUGHNE

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.

hot_rod

these cleaner kits are good for cleaning the inside of the boiler and piping. Attach and squirt into that blue valve under the Taco pumps and run all the zones for a day or two. Flush, refil, add the second can of conditioner.

Sensors go bad also, give false readings to the control board. The manual should have a chart for testing them if you have an Ohm meter?

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sunil314

How does the water system separate the HVAC water from the drinking/tap water? I was reading the warnings for the cleaner kit and it seems like it can only work on closed loop systems away from food/humans?

HomerJSmith

"How does the water system separate the HVAC (boiler) water from the drinking/tap water?" It is done by a backflow preventer. You have a double check with atmopheric vent backflow preventer.

The boiler sys is a closed loop sys. The yellow handled ball valve before the double check valve can be closed during the cleaning process for extra domestic water protection.

This is an improper way to connect the boiler cold water feed to the boiler. The drain of the hydro-separator has been removed preventing the ability to clean debris that has collected in separator to be removed. It should be repiped. The tee in the drain port pobably has the separator drain, but it won't work right. Even if you close the yellow handled ball valve before the double check and open the separator drain you could be blowing debris into the pressure reducing valve. CHANGE IT!

I am not sure that your sys piping is a primary/secondary as the best piping sys for a mod/con boiler. You might want to check that even tho the hydro-sep is supose to provide that function.

hot_rod

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.

Screenshot 2023-03-26 at 9.07.20 AM.png

HomerJSmith

The condensate neutralizer should be recharged with new neutralizing media on a periodic basis. Normally you would have unions on each side of the neutralizer on the 3/4" pipe for easy removal for cleaning and recharging.

HomerJSmith

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.

sunil314

I really appreciate all this advice and feedback. It is beyond my scope to do all this, I will hire a plumber and provide the notes you have given to get this system up to snuff.

On a + note, after taking apart the Knight and cleaning the inside of the HX and putting all the pieces back together the boiler is working as if nothing happened. I have no idea why though.

sunil314

On a separate note - it can take a good 20-30 seconds for hot water to appear, even when the indirect tank is full (measuring by the input temperature and rise on the boiler). Any thoughts on why given the photos I've provided?

sunil314

I have a honeywell AM-1 mixing valve that the top pipe of the indirect heat tank supplies into. Could that need replacing?

hot_rod

https://forum.heatinghelp.com/discussion/comment/1744524#Comment_1744524

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.

Screenshot 2023-03-26 at 4.15.41 PM.png

Derheatmeister

Increase you Pump delay from 30 seconds to 4 Minutes