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Mystery: "LOC" error message on my VXT display, yet water gauge was half full

Smag Member Posts: 2
Hello, I recently moved to an 1893 house in Rhode Island, and I know nothing about steam heating. I had something mysterious happen, and could use some tips.

During the cold snap around Christmas a few weeks ago I was monitoring the water level and the water feed display. During this cold period it went from 000 to 0.06 then 0.16 a day later. One night I noticed the house was colder so I went to the basement to check the boiler, and saw something odd:
  1. The VXT Model 24 automatic water feed counter which had displayed 0.00 for a few months, then went to 0.16, was now reading "LOC"
  2. The Safegard Model 400 low water cutoff warning light was glowing orange
  3. The water level glass gauge showed water at the normal level, half full
  4. The boiler was off and cold, despite the room being colder than the thermostat setting
It was 3 am, and I didn't know about HeatingHelp.com, so I tried the following to restart the boiler:
  1. I toggled the VXT's Feed button to On for about 30 seconds, heard water flowing, but nothing changed
  2. I tried feeding water the faster way, by opening a valve I used to refill the boiler after I emptied it
After just 1-2 seconds of the fast feed, the low water indicator light started to blink. I closed the valve. Then the indicator light went out, and not long after I heard the flames ignite and everything was back to normal, except for one thing. This is the mysterious part.

The VXT water feed display now read 185. So it went from .16 to 185 in about 7 days. Thanks to this forum, I found the VXT 24v manual, and it says what to do with LOC status if the boiler is in an overfilled or a low water condition:

"Important: The following trouble shooting steps should be taken to determine the cause of the lockout condition before restoring normal operation.
1. If the boiler is overfilled, the low water cut-off is not functioning properly. Using the manufacturer’s instructions, check the low water cut-off operation.
2. If the boiler is in low water:
a. Check boiler and return piping for leaks.
b. If no leaks are detected, check to determine if the flow of the feeder is restricted. Check isolation valves around feeder to ensure they are fully opened.
c. Check the feeder setting to ensure that it is set to feed adequate water in the event of a low water condition."

But my boiler seemed to have proper water level (not overfull). The gauge was half full. This boiler had an 18 point service check at just 4 weeks earlier and I watched them clean the pigtail and test the gauge, and presumably they tested the low-water cutoff device, too.

I inspected the radiators and see no leaks, the boiler runs once in a while, the water level is about 1/4 full when it's running (see photo, below) and half full when not running. A few weeks have passed and the VXT displays 197 (see photo).

Any clues as to the root cause of this? Which component to test first, and how?


  • Long Beach Ed
    Long Beach Ed Member Posts: 1,108
    edited January 16
    You probably know how the feeder operates:

    If the probe is uncovered, the control shuts the burner and attempts to feed a predetermined amount of water.

    If the condition is not rectified and the probe remains uncovered by water, the control will try feeding again.

    If the probe remains dry after those two tries, the boiler locks off and the display shows "LOC".

    Either the feeder is not correcting a low water condition in that it isn't passing water into the boiler or the water is leaking out. Or the VXT is messed up.

    I suspect the feed soleniod valve on the VXT is clogged and it is not feeding water, though the control is calling for it to feed. A rebuild kit is available to replace wear parts, clean the strainer and return the valve to operating condition.
  • Jamie Hall
    Jamie Hall Member Posts: 20,524
    A further thought: your low water cutoff is, clearly, working. It shut off the boiler when the water was low. That's exactly what it is supposed to do. Be happy! Now. Second, you have a serious leak or leaks somewhere. There is no way that you should be using even one percent of the water which your feeder is adding. Third, and perhaps more serious, your sight gauge is lying to you. Either the top or bottom port -- or both -- is clogged. If it's clogged, I'd bet the pigtail to the pressuretrol is, too.

    "LOC" on the feeder doesn't mean it isn't working -- what it means is the feeder tried to add water several times in a row, and didn't fix the problem. That may indicate that the filter screen on the feeder also needs to be cleaned or replaced.

    There's work to do!
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    Long Beach EdJohnNY
  • Smag
    Smag Member Posts: 2
    Thanks @Long Beach Ed and @Jamie Hall for your points of view. I checked all the radiators, and all the visible pipes in the basement. No leaks of any kind.

    I saw a This Old House video that showed someone with symptoms similar to mine. In his case they found a hole in the top of the boiler, and the steam was simply going up and out the chimney.

    So I set up a date with the same company that inspected the boiler a month earlier. I'll update here when I see their results.
  • Gordo
    Gordo Member Posts: 833
    The setting on the pressuretrol looks to be too high (just a thought, not related to your VXT issue most likely).
    Is there a visible date code inside the VXT?
    All Steamed Up, Inc.
    "Reducing our country's energy consumption, one system at a time"
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Baltimore, MD (USA) and consulting anywhere.
  • ethicalpaul
    ethicalpaul Member Posts: 4,230
    I like all of Jamie's theories and instructions. I would just say don't rely on the autofeed. Set the level yourself 1/2 way up the glass, and check it every couple days and refill it yourself as needed so you can see how much it's really using.
    1 pipe Peerless 63-03L in Cedar Grove, NJ, coal > oil > NG