I tend to agree with BT, but some simple problems could also cause the problem and could be check first in a few minutes. Look for but DON'T TOUCH any of the following:

A tree branch touching your power lines, current leakage can load the system but it's before your main breaker so your main won't trip but will snap a transformer fuse on the pole if the leakage was high enough. This is the power companies responsibility so call them. I usually see this after a storm with an instance in May of this year where a furnace starting up caused flickering and traced it out of the house to some branches on the power lines.

check for a loose connection/lug at the breaker, outside disconnect and starter lugs of the heat pump. Look for a wire with browned or burnt insulation or black wires in the connection and if you see one suspect a loose connection but DON'T TOUCH! A loose connection would drop voltage and increase current draw, and create heat melting or burning the wire insulation. and could also start an electrical fire.

If you see nothing witch only takes minutes then suspect the start capacitor on the heat pump first, if it's going bad it can cause hard starting. If the capacitor is good then would be the time to have a hard start kit installed. Just having an old HP would be the reason it would need one.

Thanks. I should have added that the Heat pump is new, only a year old. Its the first source of heat for the house, prior we only had a wood stove and electric space heaters. My husband says its not a problem that the lights flicker, but I just have a feeling that it shouldn't and want to be sure its safe. We live in a fairly wooded area, so there are always branches on the power lines.

A momentary dim sometimes occurs (there's no repeated flicker) when my HP starts, whether heat or cool but seems more often in cold weather. My electric service is 200 amp, house & system (5-ton Carrier) is 16yo. No related trouble has yet occurred ... no blown electronics or appliances. FWIW, my neighbor works (for 40+ years) for the electric company that provides the service, says the momentary dimming as such isn't a problem.

Kristina-

What's the size of your electric service, i.e., how many amps is the main breaker box?

@kudzu9

If I am reading the panel correctly, the large main breaker says 200. The heat pump breaker says 30

Thanks. With that size service you probably shouldn't be getting flicker. Just wanted to make sure you didn't have an undersized breaker box.

Typically the reason lights flicker is due to a large load firing up and stealing available current in order to start up. This effect is worse if electrical connections aren't as tight as they should be, but this isn't the only reason why... it's often times a multitude of things.

When a compressor starts up it is drawing what is called locked rotor amps. This happens with all single speed and 2 speed compressors. It is virtually eliminated with an inverter heat pump.

If normal running amps of a modern AC is 10 amps or so, LRA during start up could be 20 amps maybe even as high as 30 amps. This happens only for a split second. If it lasted longer than that, it would pop the breaker. That is why you get the flicker in the lights.

Adding a hard start for the compressor essentially speeds up the time of start up, makes the LRA draw on start up less severe, thus minimizing any light flicker.

I think if you switched to LED lighting there might be less flickering (new bulb only as when these fail they often fail by flickering, rarely do they fail all at once and produce no light.)

Because this is a heat pump, you should also check to make sure that emergency heat isn't coming on when the heat pump fires up. As this electrical load of heat strips, plus starting the compressor --- yeah that would easily be a recipe to make lights flicker.

A momentary flicker can be caused by inrush current demand when a high-current device starts up. The current demand quickly drops to normal in a fraction of a second. Has this been happening consistently? Is it getting worse? If the answers to those questions are no and yes respectively, I'd have it checked out, otherwise it's unlikely that there is a problem.

Thank you all for the explanations. I do have LED lights thoughout the home. The flicker is consistent, happenes every time the heat pump starts up but hasn't been getting any worse over time. With the heat pump turning on so many times throughout the day, the light flicker is a little annoying. I will try to convince my husband to get someone to look at it.

One solution I have come across before for this same problem is:

Check the recommended breaker size on the unit. Sometimes there is a recommended size say between 30 and 50amps. If your contractor has added the minimum size this can cause the flickering on start up of the unit. I would recommend upsizing the breaker only if the wire size is capable of the increased load. Check with the contractor who installed it and mention your concern as this can usually be rectified.

Chances are there are two breakers for your heat pump. One for the outdoor compressor and one for the air handler. In my case, the outdoor unit is 30 amps and the air handler is 60 amps.

"In my case, the outdoor unit is 30 amps and the air handler is 60 amps."

That's because the air handler presumably includes resistance heating elements that pull more power.

My compressor is a 60a breaker. The blower unit is a 60 and a 30.

"I will try to convince my husband to get someone to look at it."

Try to convince him soon to have an electrician inspect what could be the cause. A bad electrical connection causes heat. Over time the heat causes the electrical connection to become worse which causes more heat. One day all this heat burns out wires. What could be simple fix now could become a major repair at a later date

I found a bad connection wired by a licensed electrician that was glowing red hot but still provided juice to the device. You could of lit a cigar off it with ease, but because it was a commercial job using conduit and in a metal junction box it didn't cause a fire. I've witnessed more bad connections that melted the connections then I can count, and not a rare occurrence.

In fact even 12 volt wiring can start a fire because of a bad connection. My 2005 GMC pickup melted the blower motor connector and was under a recall because 100's of trucks actually had cab fires because of this.

We just installed a new heat pump and had the same problem with a few of our lights. They all had cheap LED bulbs in the sockets. I replaced them with GE Reveal bulbs and the flickering stopped. Problem solved.