Any HVAC techs out here?

[The Zigman]

Hey everyone...

I have a problem with my furnace, and thought I would ask opinions here.

I have a Rheem Criterion..

I have replaced the high fan limit switch already.

Here is the scenario...

Furnace comes on as normal...
when the heat exchanger reaches temp, the burner shuts off...
the blower continues to run, cooling the heat exchanger...
Eventually the heat exchanger cools down and the blower shuts off.
Immediatly after the blower shuts off, the induction fan comes on, and the furnace cycles again.

Shouldn't the burner cycle on and off, without the furnace completely shutting down like this? Last time I had this issue, I replaced the high limit switch, and everything was fine.

I think it should run like this:

Furnace comes on like normal..
exchanger gets hot, and burner shuts off...
fan continues to run, then when exchanger temp drops the burner should re-ignite... right?


Any suggestions?

 

[dundadundun]

sounds like flow restriction issues... unless it's been a while since you've replaced your limit switch but they shouldn't really go.

check your filters and vents. see if there's crud in there or if everything is covered with furniture and what not. if you can't clean it out from somewhere you'll have to call a professional. make sure your returns are clear of obstructions too. make sure your professional checks for collapsed lines and any obstructions. if your guy's not pointing at another issue besides the switch i wouldn't let him do any work until i get another opinion. if still no other idea i'd suspect to find a recall somewhere.

no, i'm not a tech but i have plenty in the family, have worked with them and have had the same issue. we had too much furniture over our vents... and i didn't know about half of it.

 

[The Zigman]

Hmmm.
I only have 2 cold air returns in this tiny house...
I'll take a look at them.

I did close a few of the registers, to get more heat at the far end of the house, could that be a problem?
I replaced the filter about 2 weeks ago, and can still see light through it.

 

[Madcrawdad]

Make sure you're not using a pleated filter... I've had 3 different furnace guys tell me, throughout the years, 'Don't use pleated filters!'.

I didn't think that it would make much of difference, but my brother's furnace went on the fritz a few years back, and the HVAC guy couldn't get there right away. He asked my brother (over the phone) what type of filter he used, and when the tech found that my bro was using a pleated filter, he told him to change it immediately to a regular filter. A quick filter change, and the problem was solved.

 

[dundadundun]

if your system can't support that much restriction it could absolutely be your closed registers. if they're floor registers a lot of time you can take the vent lid off and actually grab a handful of stuff or vacuum out large debris and nasty dust too. if it's in a room that gets mopped the crud gets nastier and harder to clean. you could be a major clean freak and this will still add up over the years so it's best to check every year or so anyway.

it might be time to call a chimney sweep too. air restriction can happen up there also... and it can be devastating.

a lot of times there's factors that lead to buildup in your lines. there's basically 2 ways to clean that stuff out. one is blow the other is suck. when blowing some would use something as simple as a leaf blower and cover the vent they're blowing through with cheese cloth to catch any debris. this can blow things back into your house though. the other way is with a vacuum that has a rotating spherical brush on the end. it brushes off the inside of the lines and vacuums the debris and they're able to spray a nice fresh scent for you too. this may not be necessary.

either way your issue is a serious one... far more serious than just your limit switch. the limit switch is there to prevent things like system failure, blow back and fire. if it was not kicking off you may have a more serious issue. the cleanup and mess after a blow back or fire can really send you back in your seat and hurt your pocket as well as leave you out of your own home for a bit too. so, by all means explore each possibility as best as you can and use your best judgement until you are comfortable the situation is taken care of.

if your home is getting cold in some rooms you might want to look into fixing that with your insulation. maybe it needs a once over, maybe it's just a design flaw somewhere, i can't tell from here. one thing though if it's insulation you're lacking you'll already be putting quite a bit of stress on your system already. they're usually installed and rated according to square or cubic footage (ie. according to the size of the house) so lacking in insulation in a few cracks and crevices creating air flow does a number on the health and longevity of your system fairly quickly.

it's a lot of little things to look over but taking care of them can save you big time over the long run.

 

[The Zigman]

Thanks for the info Done, I think I found the problem.

My house is about 120 years old, the furnace was added as an after thought.
The original furnace was replaced about 10 years ago with the Rheem.

The house has 3 cold air returns, although only 2 are connected to the furnace. the cold air returns are in the walls. My love seat got pushed up against one of the returns, and must have made a pretty good seal. I pulled the couch away from the return, and viola! Much more air is coming from the vents now. It is working correctly now!

I closed some of the vents because there wasn't alot of airflow from them, never thought there was a restriction in the cold air return system. I am going to re connect that other return to the furnace, maybe thats why my bedroom is always cold..

Thanks for the help! I really do appreciate it!

 

[The Zigman]

furnace is working great now..

who would have thunk it?

 

[dundadundun]

you're welcome zigman! any time i can help.