Ruud furnace clicks
October 21, 2014 7:38 PM   Subscribe

We have a Ruud Achiever 90 Plus with variable speed motor. It works great heating up the house, but when it's trying to maintain the temperature (say it's set for 65 and it's currently 65), it constantly clicks. The sound is very annoying. Does anyone know what would cause this?

We've had the furnace since 2007 and it's worked flawlessly except for this incredibly annoying clicking problem. I can't remember a time when it didn't click while maintaining the temp, but I didn't really suspect it could be a problem until recently. I just kind of lived with it.

More specifically, I think it's the inducer fan clicking. It almost sounds like it's modulating between a high and low speed. The blower motor does not seem to change speeds, and the flames remain constant (they might decrease in size just slightly when the inducer fan clicks off, but it's hard to tell).

Basically, this goes on for like 20 minutes at a time. *Click*(inducer fan slower for a few seconds) *CLICK* (inducer fan speeds up for a few seconds) *click*... ... ... *CLICK*... ... ...

The last time we had the furnace checked out (a couple weeks ago) the technician didn't see anything wrong, but of course the problem didn't happen while he was here.

Does anyone know what could be wrong, or how to fix?
posted by joebakes to Home & Garden (5 answers total)
It's probably a relay that is bumping up to the higher speed. Sometimes relays are loud. You might be able to wrap something around it to damp the sound.
posted by notsnot at 7:50 PM on October 21, 2014

I had a similar-sounding problem which turned out to be a bad controller board. Mine was also a Ruud 90 (not sure about the plus).

It was hard to diagnose. First I spent quite a while timing the cycles of clicks and whirs with a stopwatch, and wrote a list to convince the tech there really was a problem. Then the tech spent a lot of time on his cellphone talking to the manufacturer while working on the furnace.

Replacing the controller cured the problem. Luckily for me this happened right after the furnace was installed, so it didn't cost me anything. Depending on your service contract or warranty it might be less costly to skip the diagnostics and just buy a new controller,
posted by anadem at 8:01 PM on October 21, 2014

Sounds like a thermostat that should switch from one setting to another allowing for more of a temperature change in-between...

i don't know anything about these but this exchange might shed some light on some troubleshooting/diagnostic steps. Looks like at least for one person a different thermostat solved the problem.
posted by BillMcMurdo at 8:02 PM on October 21, 2014

Best answer: From the thread BillMcMurdo linked, it's clear that the problem is a design flaw in the thermostat. Here's the crucial post in that thread:
Finally . . . a quiet furnace!

Well, here you go.

The first two thermostats that Ruud had me try were UHC-TST401MDMS's.

The installer brought over a UHC-TST411MDMS (411 instead of 401).

We installed it. Set it up.

Clicking problem solved.

So, why didn't they send this out the first time? sigh
Note that the thread dates from 2008, the year after you got your furnace, so it seems very likely you have the earlier model thermostat which causes the problem.
posted by jamjam at 9:02 PM on October 21, 2014 [1 favorite]

Response by poster: Thanks, everyone. I might try to find a new thermostat (looks like the model referenced above is out of date). I've tried a few different settings (Multi-stage, single-stage) and switching some of the thermostat wires (moved V to W2, which sends a two-stage single instead of a modulating signal) and it always happens. It's so strange that it's the inducter motor that's affected, though. The flames never turn off -- I'm wondering if there could be a faulty sensor in the conductor, or perhaps at the low fan level (40%) airflow through the inducer is somehow too low.

Anyway, I think I'll try a new therm first if I can find one, which seems cheaper / easier than replacing the board. I can almost guarantee that it's out of warranty.

Thanks again
posted by joebakes at 3:32 PM on October 22, 2014

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