Hi guys. Have any of you ever had problems with static electricity ruining thermostats. Ive had two call in the last month were the homeowner said they got a static shock from the thermostat, and on one the stat just went blank, and on the other everything appeard normal, but the call for heat had shorted in the stat causing the furnace to run nonstop. Niether stats had internal fuses, but I'm surprised the low voltage fuse on the control board wouldn't blow first. Actually, I'm surprised that a static shock would cause the digital stat to malfunction, but now I've seen it. Is this a fluke, or is this a common problem. It the first time I've seen it in over ten years, or it may be the first time the homeowner mentioned getting a shock. Im not really two worried about it, just curiouse. I did mention to the homeowners that they could touch something metal near the stat to discharge the static before touching the stat.

Also, one house had brand new carpet causing static, and the other folks said they just got new bed linens and had been having fun watching the tiney sparks as they were in bed(sounds like they were having fun).

Touching the wall will work too and is good practice. No need to touch metal. Using some anti-static carpet spray around the carpet may help too.

Static electricity has very low current, so fuse won't blow.

Now, this might surprise you. Static damage MAY be REVERSEABLE. I bet you think I'm pulling your leg? Leave the stat not connected to anything for a year and it just might decide to work a year later.

To accelerate this, you can sometimes remove the batteries. Unfortunately though there sometimes is a Lithium cell internal like in the Vision Pro series and short the battery connectors for about 30 seconds.

Yes, there is a fundamental reason why it can be reverseable.

Static electricity can cause problems for sure especially with electronics. The new digital thermostats are sensitive instruments and thus susceptible to static or other unusual events. About 5 years ago we did some testing on circuit boards and part of that testing was for static disruption. This was done to test for safety and to make sure the board would fail in a no operable condition instead of leaving the gas valve actuated etc. I am sure the electronics in a digital thermostat are just as sensitive or more so. We still have that static generator machine and every once in a while a test will call for its usage. There is no way to protect sensitive electronics from static that would be cost effective. I did not say it could not be done it's just too expensive to incorporate into the price point of manufactured goods for sale to the general public.

A fuse will not protect thermostats since a static charge is usually far below the trigger point of actuation. What will work is a circuit interrupter or better yet a humidifier to prevent the problem to start with. The plastic covers along with other plastic incorporated in the thermostats afford an insulation quality but if the static is enough it will jump to a conductor somewhere in the circuit.

We still have a large brass ball that is grounded in the bench testing area along with isolation pads at the stations etc. When a student first gets into the testing program they are taught to always touch the brass ball before the work begins. Once touched the isolated/grounded floor and pads keep them from being recharged. When you are testing one off pieces of equipment you cannot afford to take a chance.

I have never heard of it doing damage to the thermostat, but I have seen lots of static from new carpets.


On the next call you get where the kids are having fun with the static have then walk around on the carpet with a fluorescent bulb in their hand as they scoot their feet on the new carpet. They will be surprised. (a short one would be best)

Thanks for the info guys. So this is more of a common problem than I suspected. I agree a humidifier would be the best option(neither house had a humidifier).
Once again, thanks.

Thank you for this information - you saved me the cost of a new thermostat and the aggravation of installing it (not an electrician!). When I touched the stat I got a HUGE static shock... then the heat kept running - but the thermostat temperature kept going DOWN. I couldn't get it to stop with the 'OFF' button. Saw your advice and took out the batteries for a few minutes - put them back in and BINGO.. it worked. Thank you so much!

Interesting, because in the past four years I've serviced a heat pump that would run continuously. I thought it obviously a bad thermostat so I replaced it. I also replaced the contactor outdoors. Everything seemed fine... for a while. The same symptom reappeared a few months later, so I replaced the thermostat again and did a continuity test on any shorting low voltage cables... they seemed good. Now a year later the symptom of the outdoor unit running on and on beyond the set desired temp. has returned. Another thermostat? Yes, it has been replaced... again, and is working properly... for now. I read this blog and remembered that the low voltage line from the indoor air handler runs into the sheet metal return duct and out again to the wall thermostat. When the symptom returns, I will now seriously consider rerouting a new low voltage cable to the thermostat. There could be something happening around the return duct and cable. Thanks for this food for thought.

I've made calculators, car clocks, glucose meters, bycicyle computers come back to life.

Semiconductor physics tells me it happens and is non-destructive.

Engineering tells me how to fix it.

The bean counters tell me NO!