The Trane 95XV is a gas furnace and is 4 years old. Periodically or randomly we are recently hearing a thump or a boom as the furnace runs. It is not heard at every run, only some runs. Maybe more frequent when as it shuts off. Any ideas what this could be? Thanks for your help.
To start with: is it a combustion noise or mechanical noise? If it is combustion related it could be anything from improper gas pressure to after burn when the unit shuts down due to incomplete buring process. If it is mechanical it could be fan or draft motor related. Either way it sound like it's time to have the unit checked and serviced by a qualified hvac tech.
Stan, thanks for the reply. I'm like you, wondering if the occasional noise is combustion or mechanical? Since my first posting, I have noticed that the noise seems to only occur when the outside temperature is below freezing (32°F). I have also discovered a small condensate drip / leak in my PVC combustion flue pipe. The leak is located at a joint for a bend, the bend below the "Y" which joins the flue pipe and the air intake pipe. The "Y" is in the attic, just under the roof deck. The drip is not always evident, but is most apparent as the outside temperature gets colder, say below freezing. My plan is to wait for warmer weather when I can open up some panels in the unit and try to find the problem. Your suggestions are appreciated.
First, you will need to know if it is a mechanical noise or an ignition noise. If it is mechanical, it may sound like a metalic clicking or banging when the blower motor comes on or goes off. If it is ignition related it will be a puff, boom or banging when the burners fire. Either condition is beyond the normal homeowners ability to repair unless you have some mechanical kowledge and an understanding of the sequence of operation of the furnance. If you can give me any more data of the problem such as, when it happens, exact sound I will be glad to assist you as much as I can.
I am guessing here but it sounds like you may be having a freeze up problem @ 32 deg. ambient temperature due to condensation and a restriction in the trap causing improper combustion and exhaust. The leak may not be a leak.It may just be condensation from the cold air and warm exhaust pipe. This is also refered to the dew point of the air.
Also, if it is not causing the furnance to fail to operate properly, I see no reason why you can not wait until warmer weather to check it out.
Thank you for the added confidence. I will keep listening and pondering what I am hearing.
You are guessing the same thing that I am. My problem is that I only understand the general features of the furnace, such as a freeze up problem in some damper arrangement, along the combustion air pipes. This is the first high efficiency furnace that I have owned. I am certain that I have a leak at the pipe joint. I checked for condensate on the outside. The pipe is for the exhaust side, thus it is "warm" on the outside. Stated otherwise, the condition on the outside is not right for condensate. The reverse will be true on the inside, thus the condensate is leaking out of a joint, where the glue was incomplete. The leak is only sporadic and when it is colder than normal, thus more condensate.
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