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[smithbr]

Hi
My furnace is out of commission until next week.  We'll be around 15 F tonight.  I want to keep the loop from freezing.  My OWF feeds house; thermostatic valve is first element at entry.  Loop then feeds HX in propane furnace, and sidearm heater for HW.  I had hoped keeping the loop running would backheat the outdoor end enough to keep it from freezing by sucking heat from my propane furnace, but as I read the description of the thermostatic valve, it won't open the loop to the furnace unless the water is hot enough.  So I'm left with the only heat input to the outdoor furnace part of the loop being from the circulation pump.  Is that correct?, and if so, is there a way to override the thermostatic valve to keep the loop open?
Blair

[schoppy]

What type of thermostatic valve is it? Is it actually operated by water temp like a hydraulic valve or is it electrically operated by a sensor? If the first then you would probably have to remove it and install piping in it's place. If the latter you should be able to do a work around with an alternative power source. 

[Roger2561]

Schoppy - The thermostatic valve operates like a thermostat in your car, it relies on a certain temp, in this case 150 degrees or greater before letting the heated water through.   

[Roger2561]

Blair - When I installed my thermostatic valve, I put drain bibs on either side of the incoming pipe.  If the time comes when I have to replace or service it and I don't want to have to shutdown my OWB I can simply connect a washing machine hose to the bibs and bypass the thermostatic valve.  Roger

[RSI]

If it is only below freezing at night then just letting it circulate to the thermostatic valve is probably fine. I thought I had read that a small amount of water will still circulate past it but I could be wrong.
If the water temp does get down in the low 30's you could just put an electric space heater in the firebox.

[smithbr]

Well, last night was -9 C - that's about 16 F; today we'll peak at 34 F.  Made it through the night with no problem, pump running and TSV seems to pass a small amount even at water temperature of 30 C (84 F); CB calls it a "trace" flow.  I suspect my propane furnace ran a lot more than it would have, but that's small potatoes.  So we seem to be okay.  Not sure what I'll do about the TSV longer term, as I'm not sure I want to try the same experiment at -35 C (-30 F), which we see every winter for a few nights.  But my first priority is to fix the OWB.   Tuesday, Wednesday we'll see -10 C again.  Not sure I'll get parts for the OWB that quickly, so I'll be calling for a propane topup Monday.
Thanks to all for the ideas, esp. Roger.
Blair

[Pointblank]

From what I was told, there is some residual flow, even when the valve is closed.  Thankfully, it sounds like its enough to keep things from freezing up on you. I wonder if these are anything like your car and you can take it apart and remove the thermostat to restore full flow?

[Walleye]

There is a small amount of flow through the valve. Mine is set up like Roger said, I can bypass the valve with a hose if I have to. A friend with a 5036 told me he just put a 200 watt light inside his one time to keep it from freezing.

[smithbr]

Update
Water and reaction chamber TCs were fine.  Controller had lost it's mind.  Swapped in a new one ( Thanks, North Star!!!!) and we're warming up now.
Thank you to everyone for your comments.  The loop was perfectly happy, holding in the low 80 F range for the last four days with just the pump running.
Blair Smith

[Roger2561]

Blair- Great news!  Happy to hear you're up and running, providing heat again.  How much did they hit you for the controller?  Roger

[smithbr]

Well, for a controller AND a water TC, just south of $600 Canadian pesos.  Not going to look at the conversion.  My dealer is looking into warranty replacement possibility, so I may get some of that back, though at a minimum I have to cover shipping the old one back in that case.

Blair