Sputtering burner

rswham

Carrier Model 58MVP, installed in 2002. New igniter in winter of 2015. Heat exchanger replaced in Fall of 2015. Both of these problems occurred within two months of passing its fall maintenance check.

This winter, after another "pass" of its fall maintenance check, got code 14 failure. Brought in a new HVAC company - a "Factory Authorized Carrier Dealer" - who diagnosed a faulty flame sensor. The replacement failed a month later and was replaced a second time. Each time they cleaned the burner, which they found "slightly dirty". The invoice for the second replacement stated that if the problem continues, the "ribbon burner" needs to be replaced.

Unfortunately, I was out of town on both these occasions, which of course were off-hours service calls. So this information is via my wife, who was home, and from what I've gleaned from the invoices.

Now, though the furnace is working, there is a disturbing sputtering sound coming from the burner area when it's firing (even in low-fire). Here's a link to a video on Dropbox on which it can be heard - and you can see how it makes the sight glass dance around a bit:
https://www.dropbox.com/s/wwmiec35seoxdtk/20170113_163116.mp4?dl=0

Any thoughts? Thanks in advance.

lchmb

I dont have a dropbox acct so cant listen to it, but what your describing sounds like it's firing back in the tube. It could be an issue with the tube or it could be a gas pressure issue. Are you on natural gas or LP?

rswham

Thanks for the response. It's natural gas. Unfortunately, the video file is too big to upload. I may be wrong, but I don't think you need a Dropbox account for the link to work.

Paul48

If you put your finger on the sight-glass, what do you hear?

lchmb

I would be checking the incoming gas pressures and manifold pressure. There is also a screen where the air intake comes in. Make sure nothing is blocking that. When the unit was serviced did they use an analyzer to test the flue gasses?

It could just be the glass causing your issue...like Paul said, push against it and see if the noise disappears...

rswham

Y'all were absolutely right! It WAS the sight glass making all the noise. While I'm standing there with my finger on it, The Woman of My Dreams says, "now if you let go, does a Coke come out?"

So obviously the seal around the sight glass (plastic, really) has failed. Right now it's being held still with a couple thin strips of duct tape. What should I really use to re-seal it?

Thank you so much! I'm so glad I posted this here. Woulda felt pretty stupid to pay for a service call for that!

Since I obviously have a couple experts here, may I ask another question? Good. Thanks.

We've operated this furnace on low-fire only for the last ten years or so. This was at the suggestion of "Company A" when we were having problems with the high-fire mode roasting certain parts of the house while leaving others cold. ("Company A" is the company that installed this unit in 2002 and has maintained it up until the last two service calls.) Their suggestion seemed to work - the house was much more uniform in low-fire only. Well, when we brought "Company B" in for the last two no-heat situations (on weekends, of course - and Company A was unavailable) they claimed that running in low-fire only is actually detrimental to the unit - and may have contributed to the flame sensor issue. My question is whether that sounds reasonable or bogus? I'm thinking "bogus," because the Owner's Manual itself describes how to lock-out the high-fire mode. (It's back in dual mode now, at Company B's insistence).

Thanks again for your help!

BobC

This copied from a previous post I made on another thread-


You can do that yourself, pick up a new sight glass and a set of rubber washers and the thin brass washers that go with them. Do not take anything apart till you have all the parts in hand. make sure you get the right diameter and length of sight glass.

This is best done with the boiler off. Turn both valves off, loosen the nuts and remove the old and replace with the new.

https://www.amazon.com/Crown-Packing-everything-repair-leaking/dp/B013ID4M40/ref=pd_bxgy_328_2?_encoding=UTF8&pd_rd_i=B013ID4M40&pd_rd_r=AWVCA5A8RTWZ5BWE3T2B&pd_rd_w=pa7Kg&pd_rd_wg=CzP7Z&psc=1&refRID=AWVCA5A8RTWZ5BWE3T2B

be sure you have a new sight glass on hand because they are very easy to crack.

Bob

JUGHNE

Bob, this is a different type of sight glass.....better read the whole thing.

BobC

Never mind

Right you are, i had looked at that a day or two back but forgot it was on this thread.

Bob