Snow Melt Thermostat - How to stop call for heat below 40F

hotpotato1974

Good day everyone! This is my first time posting on the forum, but I would like to send a thank you to everyone that uses this site regularly. This is an awesome resource, and I’ve learned so much when researching my project build.

On to my current issue. I just finished installing a three loop driveway radiant snow melt system with a dedicated Rinnai boiler. My last step here was to select a wi-fi thermostat to control the snow melting remotely. I called Tekmar to discuss options for a simple heat only option using a slab temperature sensor only. The internal room temperature sensor is disabled in this configuration. As I am not using an aerial or moisture sensor, they suggested a Tekmar 561. Great, I just finished installing the thermostat. Here’s the problem: The thermostat calls for heat any time the slab temperature drops to 40F or below. In the “Away” or OFF mode, the thermostat still calls for heat any time the slab temperature sensor falls below 40F, as a means of automatic “freeze protection”. Obviously, it is not an option to keep my driveway heated to 40F all winter when there is no snow or ice present. Do any of you know of a way to prevent the thermostat from calling for heat unless I specifically ask it to come on? Or, is there a way to disable the freeze protection setting, or set it lower than 40F? The idea for my driveway snow melt system was to be able to turn the system on remotely via wi-fi when traveling or out of town. The slab temperature sensor is just a means to turn off the system when the driveway internal temperature reaches a set point of approximately 45F. Is there an option to have a thermostat just be truly OFF unless you ask it to turn on? I am lost for ideas, and greatly appreciate any advice or knowledge that you may be able to share.
Thank you,

Aaron

GGross

Could you control the boiler via wifi and just turn it on/off as needed? let a 3rd party pump control operate your snowmelt pump so the thermostat still calls to circulate below a certain temp. The dedicated snow melting controls have the options you are looking for but generally make use of a snow and ice sensor, I am surprised Tekmar didn't recommend one of those?

ratio

I didn't see any mention of that feature on the manual I downloaded, let alone a way to turn it off. I really think you need a real snow melt controller with a snow and ice sensor if you want it to Just Work.

Barring that, if you use the Tekmar remote access app with that one stat alone, I do see a way to control it. Use the "Away" contact to manually turn the system on and off. The logic will be unintuitive (Away mode on turns the snow melt system on) and you won't have temperature response (which you don't actually need anyway), but there's only two contacts in that thermostat, and we already know the other one isn't suitable. The reason you can use this method if you have only one thermostat is that Away mode is global to all the stats connected to the app—if you want the snow melt active you aren't likely to want the rest of the system to go to sleep.

hotpotato1974

Thank you for your input and advice Mr. Gross and Ratio.

Mr. Gross- Tekmar recommended this 561 model because I am not using the aerial or in-ground moisture sensors. I wanted a manual on system via WiFi, with just a set point slab sensor.
This more simple thermostat was sold as the solution, yet it was a poor choice unfortunately.

Mr. Ratio - Thank you for the advice, however, when Away mode is set to OFF, the thermostat calls for heat at any temperature of 40F or below. The lowest thermostat set point is 40F. If I set Away mode ON, the thermostat still calls for heat when the temperature reaches 40F or below, for freeze protection. This is a tough situation, because I cannot return this thermostat. I believe that I will have to plug the boiler into a WiFi plug and turn the boiler OFF completely when not in use.

ratio

What I mean is to use the Away contact to turn the system on instead of the W1 terminal. As you found out, the W1 terminal has additional logic that makes it unsuitable for your usage. The Away terminal, at least from what I can see, is a plain old contact that makes when you turn Away mode on and breaks when you turn Away mode off, from the app or keypad. It'll be a manual process to turn it on and off, but you will be able to turn it off…

BTW, 45° sounds a little warm for a residential snow melt. I think they keep helipads at 40°.

hotpotato1974

Hello Ratio,

I appreciate your expertise on this. I think it’s probably over my head in understanding what you are saying to do with an Away wire. I have included a picture of the wiring to the thermostat I have right now. I ran an 18/3 wire along with the slab sensor to the thermostat. I have a jumper from R to RH1. I am not using an Away wire, because I do not have a relay or additional thermostats on the system per Tekmar. I apologize for being a dunce with this stuff, but it is fun to learn new things.

Also, thank you for the temperature setting recommendation. I have the slab sensor in between the pex radiant loops underneath driveway pavers, so I wasn’t sure how hot it would need to be measuring four and half inches below the surface to actually melt snow and ice in surface conditions. We haven’t experienced snow and ice yet, so I have yet to melt any ice crystals! Thanks again for your advice.

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hotpotato1974

This is what my overall system looks like:

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ratio

Move the white wire from the W1 terminal to the AWAY terminal. Then, to turn the system on, set the thermostat to Away mode from the screen or the app. When the snow is melted, take the thermostat out of the away mode.

It's not perfect, but it will allow you to turn it on or off via the app.

It's really not the right stat, I don't know what Tekmar was thinking when they sold it to you.

hotpotato1974

Thank you for the explanation, I will make the adjustment. I called Tekmar technical support today, and they expressed remorse in recommending the 561 thermostat. They are going to visit with the engineers to see if there’s a way to override the 40F freeze protection setting. If not, they said they would work to get me a newer model set point thermostat at their expense. I believe they said it is the Tekmar 150. We shall see, but thank you again for helping me with a solution I can put into play right now. This site is awesome and the people here are awesome. Thank you again!

hotpotato1974

Just to close this out, I wanted to say that Tekmar apologized for the initial tech recommendation, and offered to send me a new model set point thermostat, free of charge. I thought the great customer service was definitely worth noting as it’s so rare these days. Thanks too, to Ratio and Gross for sharing their knowledge and providing outstanding advice. It’s a great community here, thank you.

ratio

Thanks for letting us know how it went!

GGross

I am not sure the 150 is what you are looking for either, it doesn't have built in wifi control. It will regulate temperature at a sensor and is either on or off. It will let you set a lower setpoint than the 561 I believe, but it sounded more like you were trying to be able to remotely operate the system?

GroundUp

Perhaps a simple WiFi outlet or switch to control 120v to the boiler itself? The thermostat can call all it wants but if the boiler has no power unless you command it to be powered up, there would be no unwanted run time

hotpotato1974

Thanks again everyone. Tekmar sent me the 170 model, which has WiFi capability. The new thermostat is working great and is exactly what I needed for my snow melt application. Hope you all enjoy the upcoming holidays.

gaco

Thank you for posting this. I was having the same issue. See below for my solutions and photos:

TLDR: how to override freeze protection on Tekmar 561 with floor temp sensor when using for outdoor snowmelt. Steps: enable “INTERNAL ROOM TEMP SENSOR”; ensure thermostat is located in a place with temp above 4.5C; set a schedule with temp below thermostat location temp; set any temp above thermostat location temp as a schedule override (which will revert back at whatever time set on you schedule); consider adding max slab temp.

I have the same wiring configuration as you. I did try the w1 to away swap suggestion but that did not allow the system to call for heat.
I have an outdoor slab and shop on floor heat (two thermostats) that run off a glycol with heat exchanger from boiler and a house with multiple zones running water. The boiler also heats domestic water with another exchanger. This is to say that adding a smart switch was not going to be easy without also disabling some other system at the same time.

Without going into too much detail, the solution was to enable the indoor air temp sensor (option on tekmar 561). This caused the system to ignore the slab sensor reading -9C so the freeze protection doesn’t kickin when it’s 20C in the room with the thermostat—Fortunately, the thermostat is located in a room with relatively constant room temp. I guess the logic is setup so that freeze protection heat does not come on if your house is above freezing even if your floor is wildly cold.

As a bonus, I’ve set up a schedule to maintain the temp read by the thermostat at 15C (or at more than 1.5F/1.0C below the room sensor) with a “wake/leave/return/sleep” set at 15C and on 6hr intervals.

Now, to turn on the snowmelt, I just set a temp slightly above the thermostat room sensor and allow it to do a temp override which (according to my schedule) will reset to “off” at 6am/noon/midnight/6pm if I forget to cancel it myself. I may have to increase the time interval to actually achieve appropriate temperatures but either way it won’t stay on forever like it used to.

Alternative method to stop the system was either to pull the thermostat off the wall to stop it and reinstall to restart, or disconnect the slab sensor.

The new method is allowing me to still monitor slab temp, control the system remotely, and ensure that it actually gets shut off. I also still have control of setting a max slab temp (now set to 4.5C) and I’m hoping the heat pulse modulation mentioned in the manual works to slowly heat the slab if I set the target temp delta within 0.5C (or less than 1.5F) from the indoor temp sensor.

I still need to see how long it takes for the slab to actually get the surface to melting temp…unfortunately the slab is 8” thick, pipes at right at the bottom and the slab temp sensor is deeper than I’d like it to be.

Hope that helps someone if they cannot get a replacement from Tekmar.