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uncre8tv
join:2013-11-25
Castle Rock, CO

uncre8tv

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[HVAC] Short cycle with no error

I have a new Rheem upflow gas furnace. Installed by a semi-pro guy hired by the previous owner as a condition of my purchase of the home in September.

It will short cycle without any blink code and it's driving me nuts.

Exhaust vent fan comes on normally, flame sensor is clean, vacuum sensors are new with the furnace. Thermostat is calling for heat when it short cycles (verified by multimeter, plus it will short cycle even if I connect the wires manually)

Seems to short cycle less if the cover is off the combustion chamber, like it's a vacuum issue. But the vacuum sensors both have blink codes and neither show up when it short cycles. If I pull the vacuum hoses to the sensors the furnace will not start at all and will blink the correct error code for the hose pulled. Returns are clean and un-blocked. Heat vents in the home are clean and open. Checked both the exhaust vent and the intake to outside, both are free of debris (ran a snake through them).

Really wish it would just give me a code to chase down. Anyone else seen this with newer Rheems? The installer was beyond useless when I called him and refused to come out.

pike
Premium Member
join:2001-02-01
Washington, DC

pike

Premium Member

Can you be more specific? How far in to the cycle does it get: does the ignitor come on, does the gas valve open, does the blower start, etc.

How new is it? There should be some kind of factory warranty.

Tex
Dave's not here
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Model number of the furnace and photos of the installation would be most helpful. The more photos, the better.
uncre8tv
join:2013-11-25
Castle Rock, CO

uncre8tv

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Short cycle varies, but it completely comes on. It will blow for as little as 30 seconds or as long as all night. But to come fully up to temp is a maybe 1-in-5 chance. Usually it will cut out after about 10min, but there's no real consistency or pattern that I'm able to discern.

Pics and model # shortly, thanks.

no heat05
@myvzw.com

no heat05

Anon

Is the furnace fueled with LP or Natural? In a previous house, I had a Rheem furnace the did what you describe. When the temps were mild it worked normally but in cold or when the unit was run for an extended time, it would short cycle. The primary regulator at the LP tank was defective and allowing the pressure to drop too far. The furnace never set a code; it just cycled.
uncre8tv
join:2013-11-25
Castle Rock, CO

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Thanks. Similar symptoms (no temp dependence here) but I'm on city natural gas.
uncre8tv

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Click for full size
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Pics!

Model is RGRT. DOM is 04/13. But that only does so much for me as the warranty doesn't cover the install and I can't send a part back 'till I know what is wrong. Installer is AWOL.

Install appears clean. Filter is pristine (only been running for a few weeks). I cut the exhaust pipe to chase it with a snake and taped it back with black duct tape you can see. Pulled all debris from the cut out of the pipe with a vacuum. I'll fix it with a properly glued pipe connector when I figure out what's wrong.
You see LOTS of bends in the intake/exhaust, but a) still no code saying that's my issue, and b) no fix if I leave the cover off, so intake restriction can't be my problem, can it? (though it does seem to help a bit to have the cover off, it's not a sure cure.)

Never any blink codes, flame light works properly (off when no flame, on when flame, no flicker, no blink) and OK light always stays steady on (infuriatingly, since it's obviously not ok!)
uncre8tv

uncre8tv

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oh yeah, also forgot that when I cut the vent pipe I let it run for a day like that (not overnight, not with anyone in the basement, and windows were open) and it still short cycled the same.

jrs8084
Premium Member
join:2002-03-02
Statesville, NC

jrs8084

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OT: How do you change your water heater? Remover the ductwork and (abandoned) water softener?
uncre8tv
join:2013-11-25
Castle Rock, CO

uncre8tv

Member

pretty much yes. all that round duct work was from the old furnace and hwh. It's not pulling anything out now, so it can be trashed. The water softener (never hooked up according to PO) might be able to be slid around (angle of pic doesn't show there is decent space there) but if I was in for the hwh I'd probably yank that too.

tp0d
yabbazooie
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join:2001-02-13
Bulger, PA

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Try taking the tstat and wiring out of the equation.. Jump W to R at the furnace, and see if it will run a longer cycle.

Lack of gas pressure is a possibility, watch the burners when it drops out, if the flame gets smaller, you need to test main/manifold pressure. Need a manometer for that.

Do you have all the manuals for the heater? Check the length of both the intake and exhaust against the venting tables in the manual, make sure theyre within acceptable lengths for your model.

And get a coupling on that cut vent pipe asap. Duct tape is not acceptable.

-j
uncre8tv
join:2013-11-25
Castle Rock, CO

uncre8tv

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Thanks. W/R connect no help. Tried it before. Gas pressure is an idea, will try to watch it die (of course, when watching is when it doesn't die - Murphy's law being what it is.)

Tex
Dave's not here
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Not getting any blink codes when there is an issue with the furnace is highly unusual. Pretty much everything that can shut the furnace down has an associated code. So, I'm pretty much stumped as to the exact cause of the "short cycling". Because of that, I'm just going to ask a bunch of questions about the issue.

Can you be more specific as to what happens when the furnace "short cycles"? Does it shut down completely? Does it try to cycle back on afterwards without you having to do anything? And, you're definitely sure it's not satisfied by the thermostat? BTW, what thermostat do you have?

Does the draft inducer continue to run or does it shut off? What does the blower do? Did you notice any difference in the LED lights when it was running versus when it "short cycles"? What about the condensate drain? Is it installed according to the installation instructions because I don't see a drain coming out of the left side of the furnace like it shows in the installation manual. If it is drained properly, are you noticing any condensate when the furnace is running?
uncre8tv
join:2013-11-25
Castle Rock, CO

uncre8tv

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Thanks Tex (and everyone else) appreciate you all taking the time to read and throw out ideas.

When it short cycles it kills the flame (or the flame dies, idk) and kills the blower and then immediately starts up again (inducer, normal delay, flame, normal delay, fan - up and on again!)

I'm certain of the t-stat. It's a home-lite touch screen. Not my favorite but it's calling for heat. To remove all doubt I've run it with R/W connected and no t-stat and get the same results.

Inducer continues to run when blower is running. Blower shuts off when flame is out.

Not a large amount of condensate, but some. Drain is on the right side and appears ok to my layman's view.

Tonight I've noticed that having the cover off is helping more than usual. With cover off I can get up to temp but with cover on I get only 5 or 6 minutes of heat. Really suspect vacuum switches, but why am I not getting a code then... so frustrating.

tp0d
yabbazooie
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Bulger, PA

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if its not a big hassle, try connecting it to a different circuit.

you did confirm the length of the vent lines? added up all the feet, with straight pipe, elbows, and 45s?

if your pressure switches are normally open, most usually are, jump the terminals on the NO contacts after the fan is energized, and see if it runs a full cycle. if it has NC contacts also, might not be so easy

-j

Tex
Dave's not here
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If I were you, after the furnace starts, I would jump out the pressure switch for the condensate and see if the furnace stays on long enough to cycle off on the thermostat.
nma851
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said by uncre8tv:

Not a large amount of condensate, but some. Drain is on the right side

Noticed something (well 2 actually, one just an observation) that may or may not have any effect; that condensate drain on your discharge side - with the trap that has been made, wonder if there's just enough condensate that travels, at one time, into the trap, ending up throwing a quick "fault" but not enough to "trigger" a true fault when it restores.

2nd thing, "observation-wise", since it's not a sealed combustion chamber by itself, I'm wondering why there's an open KO on the LH side (for gas pipe). Essentially the combustion air is being sucked in from that source - the *closest* source possibly - instead of the outside air from your intake. Essentially, there's 2 different temps and pressures of indoor/outdoor combustion air is being introduced into an (unsealed) combustion chamber. *Could* be throwing any number of sensors off sporadically & quickly enough causing the kick-out (but restores without throwing the fault (vacuum v. no-vacuum, flame v. no flame, fuel/air mixing "varying" too much & kicking out, & so forth). Kinda goes along the line of a gas pressure change mentioned by tp0d See Profile as well, this being the theory of how the gas pressure is changing depending on what the furnace "believes" it needs as to it's fuel/air mix.

Personally it's just bugging me seeing that - more/less am thinking out loud here since we're "fresh eyes". Wondering how sensitive these are when it comes to these particular aspects & if that would even be enough to trigger any of the aforementioned events (with or w/out faults). EG: once blower comes on as well, if those ducts are not sealed as well as they should be, pressure *could* be thrown off then as well - maybe even messing with the RO when that lower vacuum occurs, & sucking the flame out just enough to kick it. Then again, that would also trigger a fault code so that argument could also be easily defeated...

Just speculating here on what I've seen in those pics & what "hit" me at first glance.

I agree not seeing faults is weird in and of itself... Gonna look up the manual on this model & see if it needs more than 1 fault in a certain period to trigger the fault code as well as if it self-restores (no manual intervention), no fault occurs.. Strange...
MrFixit1
join:1999-11-26
Madison, WI

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Reading this , I get the impression that when it shuts off . everything stops running , and then it resets itself and restarts ? Is this correct ?
If that is the case , it almost has to be a interrupt of the 115 feed .
If it was the control board opening a relay , there should still be 24 volts to the board , and as long as the board is good , there should be a code .

If it was me , I would hook a 24 volt test light , or a latching tester if you have one , across the 24 in to the board and see if that drops out when the unit shuts down . If you use a meter , try to use analog meter , response time of a DMM may be to slow to catch a momentary drop out .

I am sure you have it , but for anyone interested , »www.allreds.net/WS2/docs ··· nual.pdf is the link to the install and service manual .
nma851
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join:2013-10-13
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nma851

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said by MrFixit1:

it almost has to be a interrupt of the 115 feed .

Huh - You now have me really thinking about this. (BTW - I didn't catch this part you quoted - I suppose my response is deficient due to such)...

Seeing that old fuse/switch combo, piggy-backing off your post, now makes me wonder about the lack of a good connection on the HV side. We know a means for a [service] disconnect is all that's necessary (no fuse) - as long as it's connected to a properly sized breaker at the panel. If it was me, I would have done away with that switch/outlet combo or just a switch as I don't see a condensate pump or humidifier, but the OP already said it wasn't a pro install & is evident with other "little non-major things" seen.

For that fused switch: Over time, could simply be corroded ever so slightly, edison base corrosion/loose, socket-adapter loose, loose/weak fuse itself, or something else loose in the gang itself. Also, now wondering about the board - something loose there - not necessarily that 3A or 5A itself, but "in general". These boards - heck you can look at em' wrong and boom - erratic behavior or worse, failure!!

You make a good & viable point MrFixit1 See Profile - furnace conductor for 115V having possible loose/corrosion @panel & then the same possibility @ the furnace termination @ that switch/fuse combo, (with a 24v Xformer on it too going up "somewhere" for an unknown purpose - maybe a common for the stat but that could be accomplished via the C on the board - I dunno - obviously, the list goes on)... All that matters is a conductor w/out a solid connection will wreak the havoc you've described. The integrity of the conductor feeding the furnace itself could be nicked/frayed/etc. Trying to catch it is not easy either.

For my OWN insight as well as the OP's, thank you for the good post! Got the noggin's squirrel-cage going today LOL

stevek1949
We're not in Kansas anymore
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Virginia Beach, VA

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Sounds like it may be time to get an HVAC professional involved.
iknow_t
join:2012-05-03

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if it's not the gas supply, and not the line voltage, then no code at shutdown should be a bad board. it should give a code if an error is sensed. BTW, running the exhaust into the house is EXTREMELY dangerous, and NEVER should be done!!. (carbon monoxide) the exhaust is very warm, so it'll rise into the ground floor!.

tp0d
yabbazooie
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Bulger, PA

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Does your vent line have proper fall all the way back to the furnace, and you dont have any direct vertical piping, possibly at the wall?

I`ve seen a buildup of condensate get pushed to the furthest vertical fitting, and it will eventually momentarily block the flue, tripping out the airswitch, and shuts off the burners. The fan stops or slows, the condensate drains back, and the process starts over again.

a vertical rise of 2" is all thats necessary

-j