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Lockout, Low Fan Speed

akaDigger
akaDigger Member Posts: 26
edited November 29 in Thermostats and Controls

Lochinvar WBN050 I installed in 2008 has recently begun to lockout and throw the low fan speed message. Once in September and twice in the last ten days. It has always occurred during the 100% fire rate while in DHW. Reset puts the boiler back online with no issue.

The first time it did this in September I went ahead and performed the annual service expecting possibly that foreign object might have made it to the fan and momentarily slowed the fan. No sign, however, of anything at all. All wiring and connectors inspected for any issues. Close inspection of the fan itself revealed nothing unusual.

About ten days ago after the second lockout I disassembled again this time inspecting the circuit boards. Both main board and fan board are in pristine condition.

Watching the fan speed during both space heating and DHW I find the fan speed rpm to always be perfectly steady and at the exact speed one would expect, 500 rpm/ 10% of fire rate. No blips.

I suspect that the fan may not actually be slowing at all. The boiler may be sensing a false indication of a 30% or more reduction in speed.

The boiler has performed flawlessly these past seventeen years. only shutting down three times due to intake blockage as it should have. Twice a leaf, one time a small paper wasp nest.

Any thoughts as to my next move?

Comments

  • HVACNUT
    HVACNUT Member Posts: 6,282

    Manual says the next step is replace the fan.

    akaDigger
  • HomerJSmith
    HomerJSmith Member Posts: 2,628
    edited November 29

    There are two elect plugs on the fan. One is a four wire plug, usually in the back. Unplug it and the fan should run a top speed. If not, replace the fan.

    There is programing that controls the Ramp rate. You might check that.

    akaDigger
  • pecmsg
    pecmsg Member Posts: 5,271

    how dirty is the squirrel gage blade?

  • pedmec
    pedmec Member Posts: 1,055

    The hall sensor in the motor could possible be failing or more likely your bearings in the motor are failing and when they get hot they are creating to much friction and slowing the fan speed down. The hall sensor will pick up the reduction in RPM and report to the control that it is below its programmed speed and shut the system down.

  • akaDigger
    akaDigger Member Posts: 26

    The squirrel cage has a very light dusting. Very little dust. No end play. No side play. Spins freely.

    I'll try the fan lead disconnection and see what results.

  • akaDigger
    akaDigger Member Posts: 26
    edited November 30

    @HomerJSmith

    If I unplug the four wire fan lead while the boiler is running in space heating mode and fan speeds up, is the boiler actually defaulting to 100% fire rate?

  • HomerJSmith
    HomerJSmith Member Posts: 2,628

    Good question. I would suspect that it would, however, call Lochinvar tech and get a definitive answer. It is the blower that pulls the gas thru the gas valve.

    It's not that it is something that runs for more than a couple of seconds. You are just seeing if the blower speeds up to about 3800 rpm.

    akaDigger

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