Very high stack temps last night....why?

Bob, I hope you don't find that you end up having your boiler shut down more than you like. Only way you will know is to try it I guess. Will you be able to adjust setting easily for high temp shut down?

Just a thought - can a barometric damper be installed on the stack of a Woodgun?

Just asking as they can make for a very easy to use cleanout spot - just push the damper open & clean it out through that opening. Saves messing with caps etc. - could even wire it closed when not cleaning if you had to.

If not, then nevermind.

I'll be looking for something that is adjustable.
One thing for sure, I would rather wake to a cold boiler than a glowing hot pipe!

Not sure if this would work as I expect some leakage around the flap? All joints from the WG to the chimney must be sealed.

Yes - that's what I wasn't sure about. A baro isn't air tight.

Mine doubles as a cleanout spot - but I've got draft sucking from the top of my chimney and no forced draft fan.

I suppose some sort of variable speed fan setup likely isn't an option either is it? One that would ramp down as the fire dies? Sort of sounds like when the fire is down to coals, the fan is pushing way more air through than is needed which is pushing hot coals/embers where you don't want them. And likely dead ones too at other times, that then build up & eventually cause what you experienced. Might just be a nature of the beast though.

The problem is that once your sensor detects the high temperatures, the charcoal fire has already started. Perhaps you're thinking that by shutting down the combustion fan the fire will extinguish or at least not be so intense?

I think I had read previously that a variable speed fan on the WG would be very expensive? Fred, since under normal circumstances the temp does not exceed 500 I'm thinking that in the best scenario if the temp hit 550 and the boiler shut down I would catch it at a time desirable but at the very least I cut the air flow to minimize the possible fire. Upon next visit to the boiler it will be off when it should have been on and I'll know enough to pull the cap and clean out any coals in the pipe.

Bob, attached is the schematic with the fan shutoff shown conceptually. Don't know the details of your existing fan control circuit, but the alarm/shutoff contact would be wired in series with this circuit. If you wire to a normally open contact and the Tx Controller is powered off (i.e. contact open), the fan circuit would be disabled (i.e. interlocked from running). This is the most conservative and fail-safe way to wire the circuit. The $100 Tx Controller I ordered from Automation Direct has three alarm contacts.

Bob, below is a link to a 3 meter Type K TC with insertion depth of just under 4". $6.20 on Ebay with free shipping.

http://www.ebay.com/itm/New-3m-High...251?pt=LH_DefaultDomain_0&hash=item41703816ab