Remotely turn on 441 and 2400?

[stevecon]

Hi.. I'm looking into remotely turning on my 441 & 2400 Monitor heaters at my weekend place in NH. I normally set the heater to 46F when I leave Sunday afternoons. Since the heaters use a funky thermostat, I thought I could work around this limitation by tricking the sensor (thermistor) into thinking it was colder indoors than it actually is. Initially I thought if I had second sensor OUTSIDE, and a way to switch between the two sensors, I could make this work. Switching will be easy, but temperature / resistance ramp details on the thermistor are no where to be found (with any certainty anyway).

Monitor replacement thermistors for these heaters are a bit pricey at ~$25 (used on eBay) and $50+ (new). Since I have no need to actually convert a temperature to a resistance value, I thought I could get away with substituting a variable - or even better & cheaper - a fixed value resistor instead. From what I've read in the service manual, the resistance of the sensor at 77F is 10k ohms. Someone else said that 70F is ~12k ohms and at 58F is ~16.5k ohms. The accuracy of that info is unknown. Since I need to drive the heater to "high fire" from an ambient of 46F, I need to know what the resistance of the thermistor is at ~46F. I also need the temperature (and the amount of resistance associated with that temperature) that would be low enough to bring the burner into "high fire" from this 46F temperature. I also wonder if there is a temperature that is so low that the Monitor will not attempt to start?

The switching will be made possible via a wifi "smart plug" (that works with either Alexa, Google Home, or a associated proprietary app) to energize a RIB "RIBU1C" relay which will switch between the thermistor (normal operation) and resistor (produces the high fire call) input to the heater for remote starting - when triggered. I have a couple wifi cameras that I can be use to provide visual confirmation if I feel the need.

Of course, if this has already been done - I don't need to reinvent the wheel. Just point me where to go and I'll be on it! (FYI: my links in the post were removed.. those remaining were provided by the system).

Thanks in advance!

[adnadeau]

This possibility was discussed in the Monitor Heaters/External T-Stat for Monitor K-1 heater? thread a few years ago.
I suggest you Google NTCLE100E3 for the spec sheet on Vishay's thermistors. On page 10 in the right-hand column you'll find a chart of R25 thermistor values from -40°C to 150°C. (I'm guessing that the 441 thermistor might have the same specs).
Another possibility is to use the "Loss of Power-Automatic Reset" feature of the 441. This is the slider on the right side of the unit. Set it to the desiered value of 76 or 78°, & use your relay to switch off AC power for a few minutes & then turn it back on again. The heater will revert to the slider setting.

[stevecon]

Hi, Thanks for replying.

I missed the discussion on this before. I was hoping to find out for sure what the resistance value at something between 20F and 30F degrees would be. I would think sensing a temperature that is 16 + degrees lower than set point would bring the heater into high fire. I guess I'll just wire a 10 turn pot to the sensor wire and read the temperature on the display instead.

Using the "Loss of Power .." feature isn't an option, as power reliability in my area doesn't win -any- awards. This fall, the local electric utility has spent quite some time and money having a contractor do some -major- tree trimming along their power lines, so there may be hope. Setting the slider to a setting as suggested could be quite costly - but i'm sure the local mice and other small, heat-seeking animals would be content!

Thanks.

[TechEditor]

You can fake out a thermister with this: http://www.homerepairforum.com/forum...ad.php?t=12365
Have used it for years. You can fine tune the setback with a strip of velcro on the wall and the mating piece on the Thermister. By moving the Thermister up the wall away from the resister, you can adjust the amount of setback.