Mystery Device: 700W for 2-3 seconds every 30 seconds

A couple days ago, something in the house started cycling. It has been consistently using 500-700 watts for 2-3 seconds about every 30 seconds since then. All the kids were in bed and my wife and I were watching TV. 700 watts is an awful lot for something I can’t find. I’ve been in all the kids rooms and unplugged everything more than a nightlight. I jiggled all the knobs on the oven and made sure all the burners were cold. There’s nothing like a hair dryer or curling iron plugged in (or any other normal plug-in heating element).
I’d really appreciate any help tracking this down.
I have a 7.75kWp solar array, a propane water heater (exhaust fan already found), propane furnace with heat pump for AC.
I’m having trouble getting screenshots to attach, but I’ll keep trying.
This is when it first started.

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We have see Keurig coffee machines do something like this.

Thank for the response. We do not have a Keurig or other “on” heating elements in the kitchen.
This is a closer look:

It’s also interesting that the wave is very inconsistent:

There was a user that heat tape to prevent ice dams that resembled this

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Thanks for replying. I don’t have anything like that. Am I right in thinking I looks like a motor with generally a short spike as part of the waveform? 700W seems more like a heating element, though.

Those spikes usually indicate a motor, especially at the beginning of the waveform. I do have a heating element that also has spikes so it can be confusing.
What you have appears that it could be a motor or heating element to me. That’s a lot of electricity at 700 watts.
The only device I have that comes on every minute for a few seconds is a Keurig, I wonder if you have something malfunctioning?

I see it’s getting warm-ish in Virginia … this is probably a dumb question but is your AC on?
Seasonal transitions are notorious for AC-on-while-heating-is-running type issues.
You have a different heating and cooling systems so … just asking.

Do you have a well or other water pump?

I don’t have a water pump, as I’m on a municipal supply. I’m leaning toward something malfunctioning because, as I said in the original post, my wife and I were just watching TV when it started (unbeknownst to us at the time). If firgured my oldest son might have been awake, but I already checked everything in the kids’ rooms.

My heat pump is configured for AC only. It won’t run when the heat is on. I’ve double-checked that the heat is not on for either level (two thermostats, air handler has a damper to direct air between levels).

If you fridge is detected you can look to see the compressor consumption. If it’s running more than it should then the defrost could be stuck or malfunctioning. Those defrosters are usually around 500 watts or more

I just realized that my sump pump hasn’t been recorded for 5 days. I wonder if it started malfunctioning. It’s around 700 watts.
Supposed to rain this weekend, so I guess I’d better check it out tonight.
This is what is normally looks like:

It hasn’t been recognized yet, but you gave me a thought. Maybe it’s the defrost cycle. I don’t know how long that should last…

Edit: wow, my skimming your post was really bad. I guess my brain saw defrost even though I was thinking you meant compressor the whole time.

My defrost lasts 11-15 minutes once to twice a day

I would guess if the defroster is running on that cycle, even though it’s a short spike, it would seem enough to make the fridge malfunction. Perhaps.

Stuck sump pump sounds like a probable target … that’s what I intended to imply when I suggested “water pump”

Could be the float on a sump bouncing up and down. Probably nothing wrong with the pump itself but the float mechanism like a sticking toilet

Given the frequency of the cycles, you’re probably best off doing a “binary search” by turning half your circuit breakers off, waiting to see if the device continues, etc.


It was the laser printer! Seems like my wife printed some things, but it ran out of paper. I guess it was just keeping warm until someone added paper.

Thanks for all the help!


Wow, I don’t have a laser printer but I’m really surprised how much electricity they use. If it uses 700 watts for “keeping warm”, how much does it use when it’s actually printing?

For the most part they don’t. I think the key part here is that the printer was in the middle of a print job and waiting for more paper to finish, so it may not have gone back to an idle state.

My laser will “keep warm” for about 5- 10 minutes after a completed print job, and then go back to a proper idle state. Some printers you can define that a bit more. Often in a setting called “fast start” or something like that where it keeps the fuser warm so that when you send a print job, it can get that first page out a lot faster.

Screenshot of my printers fuser (Sense Detected) below. If memory serves, I sent two jobs about a minute apart in the first chunk, and then a third page around 3:22. Not detected area all the other parts of the printer (rollers, paper feed, fans etc…)


I have a Brother HL-L23600W

This was printing 3 pages and going right back to sleep: