195C? Are you sure about that? That would be 383°F.

The easiest solution for the scenario you described where the wood fired boiler is playing catch up but has not gone completely out is to set the aquastat on your "domestic burner" 20 or so degrees below the temperature where the outdoor furnace stokes. This "setback" will prevent the inside boiler from firing until hot water from the outside furnace makes it inside every time there is a demand for heat, it will also provide some freeze protection for your outside boiler should the fire go out in extremely cold temps for an extended period of time.

If all you want to do is isolate the circulator for the outside unit when it`s temperature is below a certain point, look at the aquastat and see if it has extra terminals for controlling the pump within the specified temperature range, if it does not, you can get a different stat that does. A more complicated boiler/pump controller can be installed but simplicity is generally best.

barbedwire

Yea, now thats just embarassing and serves me right for going fast and not paying adequate attention; 383F would be quite hot!

I have the "setback" adjusted as you stated and this works. There are times though that the burner is loaded by folks upon which I lack complete faith and I am looking for a failsafe that will protect my home while I'm away. The boiler is fine unheated so long as the circulator pumps are going.

I envisioned a simple thermostatically controlled switch wired to a relay that would cut the power to the circulator. As a secondary function I would like turn on a beacon indicating the switch has been triggered. Heck, I could have my PC send me an email on my blackberry, with the right interface!

I like your idea of extra contacts on the aquastat, I ran extra wires to the burner so this is plausible and would be easy.

Well, I just found it, I have been googling for a couple of days and suddenly this is #1 in my search results; wonder how they became relevant to google all of a sudden?

Anyway thanks for the input.

Here is a link that might be useful: temp controlled switch

"Therefore I need a switch that will cut power to the circulator between the heat exchanger and the domestic boiler"

"The boiler is fine unheated so long as the circulator pumps are going."

Huh.......guess I`m not exactly getting your point then because these two statements seem contradictory?

Bottom line is still the same though, the aquastat is the temperature controlled/controlling switch, any number of relays and auxillary functions can be controlled by it very simply and cheaply. You can also add an immersion well inside your home where you would install another aquastat which could control a relay that opens at a predetermined temperature thus disabling the circulator if it is simpler for you.