Furnace shuts off after 4 minutes...

Bob_28

My two year old house has a two-zone Rheem horizontal high efficiency condensing gas furnace in the attic. Other than A/C, it's just used as back-up for the house's radiant floor heating system and so it's only been turned on a couple of times. But even though it's getting an "on" signal from the thermostat, the heater comes on for only about four minutes before shutting down (followed by the fan coming on for several short intervals without the furnace going). After a while, the furnace will come back on again, but it still stay on for only four minutes before shutting down. This problem is present in both of the furnace's two heating zones (each have their own thermostats). The filters are clean and I can't find any other obvious problem.
It's possible that the unit never worked properly. Because it's a back-up system, we've just never paid too much attention but now we'd like to get it fixed. It sounds like some kind of over-heating switch is telling it to shut down shortly after starting but I don't know much about heating systems. Is this something I can troubleshoot myself or should I call a repairman?

Thanks for any suggestions you can offer.

Bob

jim lockard

cond. fur.

Condensing furnace in attic bad idea. Did one paided dearly for it. Condensing furnaces make water,water freezes in attic,drain lines freeze, is your trap in furnace dry?

Bob_28

I live in northern California and we rarely get even a frost here so there's little likelihood of a problem with freezing. Any thoughts on how I might troubleshoot this problem to understand what other things might be involved?

Bob

Don_4

furnace problem

As was already stated, check to see if the trap on the furnace drain is dry. When left idle for long periods of time the water will evaporate. This trap must have water in it for the furnace to operate properly.

don_9

on and off

Most time if the trap is not prime the furnace will not fire at all,the pressure switch will never prove.

I would check the tstat and see if it a anticapator or
cycle rate problem.

If not there it could be several other things that only a
pro would know and where to look.
Why are we using a furnace to back up infloor anyway?
Two heat plant...Why? Why?

Mark Hunt

Is there


a by-pass? If one zone calls the furnace will still produce the same amount of BTU's and will require as much air flow across the heat exchanger.

With no by-pass, the furnace is operating on high limit which is why the fan continues to cycle.

Mark H

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Bob_28

I've already replaced the thermostat with no correction of the problem and the thermostat for the other zone doesn't work either so I'm assuming it's not a thermostat problem.

The reason I have a furnace in addition to radiant heat is because we travel a lot and turn the thermostat down while we're gone. When we return home, it may take 8-12 hours for the radiant alone to bring the temp from 50 back up to 70 degrees. Since we had to have ducting and a fan for the A/C anyway, we figured adding a furnace would be a good idea. However, we haven't used it much until recently and that's why we've only begun to work on the problem.

Bob

Bob_28

Mark, how can I tell if there's a by-pass? Also, this unit is one of two 2-zone furnaces that I have in the house. Each zone has its own thermostat and cold air return. The other furnace works fine in both zones.

Bob

Dale

Drain?

If it's in the attic the drain needs a working heat tape, If you don't used the furnace too much Ice can form in the bottom of the collector box which will affect the operation of the pressure switch. We find this when outside air is used for combustion and the people keep the house cool with a large setback at nite.

Steve Miller

90% furnace probs

The problem sounds like the condensate tubes from the recup coil and/or from the induced blower are clogged. They're usually held on with pinch clamps, just remove the rubber tubes and the plastic tubes they're connected to and flush 'em out under runnng water. Flush out the trap they dump into as well. Just remember how the tubes connected and make sure they go downhill to the trap. change the filter while you're up there too.

Steve M

Bob_28

Trap check tomorrow

Most responses seemed to point toward problems with the trap so that's what I'll check out tomorrow and report back on my findings. Thanks to all those who replied!

Bob

Mark Hunt

By-pass


There should be a duct that runs between the supply and return duct, allowing some air to "by-pass" the system and keep the furnace from cycling in high limit.

If you could post some pics, that would be helpful.

Mark H

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don_9

Cycles

Hello Bob,We are all just taking guesses here as what your problem could be.

If the unit is trying to light but does not,then it could be
a dry trap,clogged drain line,no gas pressure and other things,as mention above.But most system will lock out after so many try and then you would have to kill power to reset it to get it going again.

If the unit is firing and running for four minutes then
one would assume-tsat problem or shutting down on safety.

Also as mention above,and again it hard to understand because from your post,one would think that you either have one furnace,with a zone damper system, or one furnace per zone.

So on that note I would call the guy who installed it and get him to explain what it is that you have,and while he's is there go ahead in tweak the system.

I also understand why you have supplemental heat,I just
dont understand why you need two or more heatplant to
produce the same energy that one could do.

Thanks Bob,just looking at it from budget point of view.

PAUL LOGAN

short cycling

BOB, BUMMER ON THE SYSTEM. IF I WERE TO HAZARD A LONG DISTANCE GUESS, THE FURNACE MAY BE OVERSIZED FOR THE DUCTWORK. IF THIS IS THE CASE THE FURNACE ISN'T ABLE TO DISIPATE ENOUGH HEAT FAST ENOUGH INTO THE AVAILABLE AIR FLOW, OVERHEATS AND CONSEQUENTLY PROTECTS ITSELF BY GOING OUT ON HIGH LIMIT. YOU NEED TO CHECK THE TEMPERATURE ACROSS THE FURNACE.

THAT MEANS FIND THE TEMPERATURE OF THE AIR GOING INTO THE FURNACE AND THE TEMPERATURE OF THE AIR THAT IS COMING OUT OF THE FURNACE. IF THIS TEMPERATURE IS OVER ABOUT 60* YOU HAVE A PROBLEM. YOU COULD CONTACT THE MANUFACTURER ABOUT REDUCING THE INPUT RATING ON THE FURNACE. (I DOUBT IF THEY WOULD BE HELPFUL ON THEIS.) OR YOU NEED TO FIND SOME WAYS TO SERIOUSLY AUGMEHNT THE AIR FLOW ACROSS THE FURNACE. (THE OTHER DISTASTEFUL OPTION IS TO REPLACE THE FURNACE WITH ONE THE MATCHES THE AIR FLOW THE DUCTWORT CAN PROVICE.)

THESE TYPE OF REPAIRS ARE USUALLY HANDLED BY THE PROS.

GOOD LUCK

PAUL LOGAN

PAUL LOGAN

short cycling

BOB,

BUMMER ON THE SYSTEM. IF I WERE TO HAZARD A LONG DISTANCE GUESS, THE FURNACE MAY BE OVERSIZED FOR THE DUCTWORK. IF THIS IS THE CASE THE FURNACE ISN'T ABLE TO DISIPATE ENOUGH HEAT FAST ENOUGH INTO THE AVAILABLE AIR FLOW, OVERHEATS AND CONSEQUENTLY PROTECTS ITSELF BY GOING OUT ON HIGH LIMIT. YOU NEED TO CHECK THE TEMPERATURE DIFFERENTIAL ACROSS THE FURNACE.

THAT MEANS FIND THE TEMPERATURE OF THE AIR GOING INTO THE FURNACE AND THE TEMPERATURE OF THE AIR THAT IS COMING OUT OF THE FURNACE. IF THIS TEMPERATURE IS OVER ABOUT 60* YOU HAVE A PROBLEM. THIS TEMPERATURE DIFFERENTIAL SHOULD RUN BETWEEN 30* & 50*.

YOU COULD CONTACT THE MANUFACTURER ABOUT REDUCING THE INPUT RATING ON THE FURNACE. (I DOUBT IF THEY WOULD BE HELPFUL ON THIS.) OR YOU NEED TO FIND SOME WAYS TO AUGMENT THE AIR FLOW ACROSS THE FURNACE. THIS IS DIFFICULT BUT POSSIBLE. (THE OTHER DISTASTEFUL OPTION IS TO REPLACE THE FURNACE WITH ONE THAT MORE CLOSELY MATCHES THE AIR FLOW THE DUCTWORT CAN PROVIDE.)

GOOD LUCK

PAUL LOGAN

Unknown

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Dean

Short cycling

Bob,

Sounds as if your furnace is short cycling on the limit control- either the furnace primary limit, or depending on what brand of zoning system is used, a supply air temperature sensor could be cycling the furnace. If it is the furnace primary limit, you have a temperature rise issue. If the zone system SAS is the reason for cycling, you may not have enough (or any) by-pass air capability or even SAS temp setting is not set up properly on the zone control board.
In any event, I would call your heating contractor to check this out. We can speculate for weeks what could be going on, while your HVAC contractor should be able to diagnose and repair your system promptly.

Thanks,
Dean Meece
Lennox Industries

Dave_16

Are you guessing at the flame on time???

Or have you actually timed it? It sounds as it maybe as simple as a dirty or bad flame sensor....assuming you have electronic ignition, what's the furnace make ? what fuel are you using? On newer furnaces evrything is controlled by a circuit board, including the fan on time. Let me know

SteveT

filters

> Bob,

>

> Sounds as if your furnace is short

> cycling on the limit control- either the furnace

> primary limit, or depending on what brand of

> zoning system is used, a supply air temperature

> sensor could be cycling the furnace. If it is the

> furnace primary limit, you have a temperature

> rise issue. If the zone system SAS is the reason

> for cycling, you may not have enough (or any)

> by-pass air capability or even SAS temp setting

> is not set up properly on the zone control

> board. In any event, I would call your heating

> contractor to check this out. We can speculate

> for weeks what could be going on, while your HVAC

> contractor should be able to diagnose and repair

> your system promptly.

>

> Thanks, Dean

> Meece Lennox Industries

SteveT

filters

Did you check the air filter in the furnace? Start with the simple stuff first.

Delbert Nicks

Furnace problems

Hi Bob:

I am just a home owner and a DIYer. We had the same problem as you are telling about the furnace coming on and going off in short cycles. Ours was a new factory built home and the furnace would come on and off every 6 min as I had timed it several times. To make a long story short we put on a programmbl Thermostat and that has taken care of the problem. I think the problem was the heat would get up enough to break the points on the stat and than would come back on. Now the furnace runs for quite a while but it has to get the house up to at one degree above the setting to shut off. We live in Colorado and we have some cold weather and it is working fine. We have had a heat loss and we require about 60,000 BTU's The furnace is a 72,000 BTU. We are going to change and put in raidant in floor but will keep the hot air for a while to make sure the hot water works good. I would like to know if this takes care of your problem also.
Delbert

tombig

Back up system

I agree with all who posted that a backup 90% in an attic is a bad idea. Usually theres not a problem if used for primary heat. As it get's colder out it runs more and keeps the periferals unfrozen.

If this is a backup, how is it controlled? Does the radiant have it's own stat? Maybe you replaced a two zone w/ a one zone stat and it's now miswired?

A pro needs to look at your system and make some recommendations. You have multiple issues probably.

Bob_28

Goebig, if you read my earlier posts, you'll find that:

1. Freezing isn't a problem in my area
2. The F/A furnace was only installed because of the lag time required to heat the house with radiant if we've been away on vacation and turned the radiant thermostats down; besides, we had the ducting for A/C anyway.

The two heatings systems (radiant and F/A) aren't linked in any way. The house is 7,100 sq. ft. and has 14 radiant thermostats and 6 F/A (heat and A/C) thermostats. Two of the four F/A systems are two-zone systems.

Sorry if my earlier posts didn't make this clear but I didn't want to get into issues that weren't central to my problem, i.e., one of the two-zone systems' furnaces isn't working correctly.

Thanks again to all who took the time to share their expertise. I'm having the installer come out to look at the situation.

Bob

Dale

Animal nest

Be interesting to find out what the tech finds but often a bird/bee nest of some sort partially blocks seldom used pipes.

tombig

Bob

I did pick up that you were in a temperate clime, I made those comments as a generalization. Some forced air systems are 2nd staged at the stat and that issue hadn't been addressed so I did.

Good luck w/ the diagnostic/repair

Kevin_12

Bob

I agree with the over heating situation. Here is a test. Try putting the blower to ON at stat, this might give you A/C speed which generally is higher than heat. Call for heat on all zones so all dampers are open. Does the furnace run longer now? Put a thermometer in the return air at the furnace, or where the filter is. Then measure the supply at the furnace. Is the rise over 70 degrees? it could be a drainage problem also, is the furnace level all directions? Cut the drain pipe and watch for water flow. I assume this has A/C attatched to it. The evaporator coil could be stopped up with dirt. The manufactures label where you find the model # will tell you the max. rise the furnace can operate at. If it still overheats assuming that it is, 1 more test, run furnace with blower door off, then recheck the temp. rise. alot of furnaces don't have enough return air!