I have a very old gas wall heater (probably about 40 years old). When the motor for the fan turns on, there is an audible "click" and the HDMI signal is interrupted for a couple of seconds (i.e. the screen goes black), then the picture comes back. When the fan turns off, there is a slight flicker on the screen, but not all the time.

  • The heater and screen are in the same room. I'm not going to move the screen to a different room and freeze to solve this problem!
  • The heater and screen are plugged into different power points
  • They are 3 metres away from each other, and I don't have any other convenient location for the screen
  • I am using a single HDMI switch for different devices
  • My DVD player uses a three wire RCA cable (red-white-yellow) and doesn't receive (noticeable) interference, being a less sensitive analogue format
  • This only happens when I'm using HDMI, not any other type of connection

How can I either or both:

  1. shield the wall heater to prevent it "broadcasting" interference
  2. shield the HDMI cables and switch to prevent them receiving interference

4 Answers 4


I think you need to check whether the actual issue is interference or the fan turning on/off causes a power issue that doesn't turn off the TV or other equipment, but causes a dropped signal. If it's the latter, you would need something that "levels" your power, which a good uninterrupted power supply (UPS) should do.

  • This solution looks like "a good thing"™ to do anyways too.
    – Stan
    Commented Sep 20, 2018 at 20:05
  • I don't have this problem when watching a DVD on the same screen. It's a smart TV, so if the power goes off temporarily it has to reboot, which takes longer than a couple of seconds (more like 10-15 seconds) and looks very different. When this happens, it just loses the HDMI signal for a couple of seconds.
    – CJ Dennis
    Commented Sep 20, 2018 at 23:49
  • It doesn't have to be the the TV, if the signal strength from your PC, video game console, VCR, whatever dips, the HDMI signal might drop. Since your signal drops are discrete and not constant, it sounds more like a signal spike than interference. You could try expensive shielded cables, but those are usually a waste of money for digital signals.
    – pboss3010
    Commented Sep 21, 2018 at 11:45

Try putting your electronics on a different house AC circuit (fuse) from your heater.


A digital signal can still be disrupted by EMI interference. Hdmi standard should have shielding in the cables but the cable manufacturers may not implement it.

Did you ever try to move the source device out of plane of the interference or interfering source? What about different cables?


There's a bad signal coming across -- and it could be coming in as a form of radio, or through wall power. If you move the heater to a different house AC circuit and it goes away, it's coming in through wall power. The pro audio community has some $50-$100 widgets that can effectively filter such signals. A good IT power conditioner will do just fine also, though those are usually more expensive, and also do more, the widgets designed for audio do not protect against power surges etcetera, whereas IT power conditioners do.

I asked about specific product recommends; thank you, Glorfindel, for the correction.

An example of a pro audio widget which filters power well in my experience, is the Ebtech Hum X:


Filters such as the above can filter a whole lot of power, most of them can handle the whole 1300 watts or so which a standard 15A wall socket is good for (one should not run a 15A, or really anything powered, at 100% capacity for long, with certain very specific exceptions...).

IT power conditioners do a lot more, and protect a lot more, are generally more expensive...but can usually handle much less power. The best of these are probably the ones called "isolation transformers", some made for IT for general protection, and some made for medical purposes, to make sure stray signals don't get into EKG and the like. I buy these used, either surplus sales web sites or more recently from eBay. Tripp-Lite is a brand I've used recently, there are others worthwhile too. You do have to watch the watts on these.

I do not have any affiliation with any vendor, designer, marketer, or builder of these products, or any web site cited.


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