Lockout, Low Fan Speed

akaDigger

Lochinvar WBN050 I installed in 2009 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 sixteen 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?

HVACNUT

Manual says the next step is replace the fan.

HomerJSmith

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.

pecmsg

how dirty is the squirrel gage blade?

pedmec

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

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

@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

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

Over a month later and (fingers crossed) the boiler has performed as it should. No more lockouts.

I unplugged the fan when it was firing at 100% (DHW) rate and 5200rpm on the blower. It did speed up, quite a bit.

Lochinvar Tech was helpful. Though I failed to ask my default question. The tech suggested that since it was an intermittent fault, and the fan responded to the disconnect as it should, the likely suspect would be communication wiring and connectors. (90% likely) Boards, both main and fan typically don't have intermittent failures.

Perhaps, since I had disconnected and reconnected the wiring at the main board while inspecting during the second disassembly, this may have corrected a weak contact point. Hard to say since it all looked great to me at the time. However, since the boiler continues to work, I'm not inclined to fool with the wiring again at this time.

Talking with my supplier's sales rep we find Lochinvar replacement boilers (next gen 55k BTU wall hung) can be scarce. Both reps suggested a readily available and inexpensive Navien NHB-55 unit. The main upside would be it is a very easy installation compared to the quite difficult adaptation of the reconfigured Lochinvar. Also, in an emergency, the Navien is stocked locally ten minutes away.

Dennis

It definitely sounds like the board in the fan motor is failing. Don't jump down my throat for this bit of advice but, all the fan boards in similar sized boilers are the same. If you have access to a fan where the wheel failed or any other similar model fan that might not mate up to you boiler you can swap out the circuit board in a pinch. The plastic housing has a couple screws, the small plastic fan that can be pried off. The circuit board has two or so screws and pull off pins connecting it to the motor. In a pinch similar blowers with differing mounting plates can be used by swapping plates. I had a Laars Mascot (Baxi) boiler fan fail on a 5 degree day, having a Munchkin fan in stock on the van, I switched the mounting plates and had the heat on in an hour. Confirming operation with a combustion test. The Laars part showed up 8 days later, costing $150 less than the Munchkin fan the Laars became the new fan on the van.

akaDigger

My luck may be running out. After six trouble free weeks, the boiler did the lockout again. Five times in the last ten days. Some I tried to blame on the frequent one second power interruptions we've experienced this past week due to the ice storm.

I had been looking for a fan, used, NOS, open box new, priced much lower than new with little luck.

In a pinch, I'll have to go with a Navien NHB 55k. Most easily adaptable and readily available.