VC Large WinterWarm Air Probe/Thermostat Checking and Replacement

  • Active since 1995, is THE place on the internet for free information and advice about wood stoves, pellet stoves and other energy saving equipment.

    We strive to provide opinions, articles, discussions and history related to Hearth Products and in a more general sense, energy issues.

    We promote the EFFICIENT, RESPONSIBLE, CLEAN and SAFE use of all fuels, whether renewable or fossil.
Not open for further replies.


New Member
Nov 2, 2015

I apologize if this is covered elsewhere but I couldn't find anything after some extensive searching.

I have a Vermont Castings Large Winterwarm that has worked well over many years. Recently I've noticed a lot more smoke coming from the chimney when the damper is closed and there's significant build-up of creosote downstream of the refractory box and catalyst and in the chimney itself. The fire burns well but it appears that there is no secondary flame after the catalyst (I used to be able to hear this burning as well). I've just fitted a new catalyst and the problem persists.

I think there's no air getting into the secondary combustion chamber and suspect either the air probe (or thermostat as I've also seen it called) or the air flap mechanism it controls. I can find no details on how to check the operation of this assembly or even how to access it for inspection or replacement. Could this be responsible for what I'm seeing? If so, how do I get to this? Do I need to remove the insert from the fireplace (a royal pain) or can I access it from the interior of the insert? The whole air intake mechanism is rather a mystery - there are no drawings or description to help me find if it's blocked or broken.

Thanks for any help.



Master of Fire
Sep 2, 2008
You will need to pull the insert. Some models have an access panel on the back, some do not. If you don't, you will need to remove the convection jacket that's around the firebox. It's a real pain!
Last edited:


Staff member
Nov 18, 2005
South Puget Sound, WA
When the catalyst was out, did you inspect the secondary probe with a mirror? Is it in good shape?
Not open for further replies.