Failure analysis: Hygger heater controller, stuck on.(HG-802)

[UncommonSense]

For context, this isn’t my heater/controller combo. It belongs to a local reefing buddy whom messaged me this morning to the tune of “so I just woke up to my temp controller reading 88F, with 86F on an external thermometer…”

Thankfully, there was no loss of life!

— So, this Hygger HG-802 temp controller and 500w HG-902 “titanium” heater were installed August 22, 2025. The tank is a Fiji95INT with Fiji 36sump; estimated 100g actual operating volume… the controller has a pretty ugly dead band of 1.8 degrees F (so this isn’t a old controller, or one which was short-cycled daily…)

Here’s how the “titanium” heater tube looks ~8 months later:

That speckling you see isn’t debris, it’s etched into the metal’s surface… the tube feels rough like a higher grit sandpaper, you can’t scrape it off with a nail, either…

This heater was mounted in the sump return chamber, lower in height than the return pump inlet, specifically to prevent it from ever running dry…

I just did some research on this phenomenon and found that some extremely cheap off-brand heaters have been known to plate stainless steel tubes in titanium… now, i’m not certain that’s what we’re seeing here, but I do know my 10+ year old Finnex heaters don’t have any of this corrosion-like surface finish…

On to the controller:

I set it to a low target temp, stuck the probe in warm tap water, and waited for it to turn off…

Yeah… this controller’s just stuck on. It refuses to turn off the 120V outlet…

So, on to teardown:

These are the prime suspects any time switched power won’t switch, relays:

Now, to see if my suspicion about contacts welding is correct:

Yep… this “20A/125V rated” relay welded its contacts at <25% of the (apparently rather optimistic) claimed amperage rating…

The eagle eyed among you might note the absence of any silver alloy plating on those high voltage contacts, too…



Simply put, this is a PSA to those of you whom are looking at, or have one of these heaters/controllers…. They are not safe for your tank, or your home.

 

[TangerineSpeedo]

Nice write up

 

[Gumbies R Us]

Thank you for sharing the extensive work you went into to see how these controllers work!

 

[xiaoxiy]

Could I send ya another (functional) hygger heater, for teardown purposes? I’m curious as to whether all of their controllers/heaters are shoddily made.

 

[Bear22]

There have been some serious issues with Hygger heaters. Some of them have posed electrocution hazards.

See King of DIY (Joey Mullen) via YT and his podcasts with these Hygger heaters.

 

[UncommonSense]

Could I send ya another (functional) hygger heater, for teardown purposes? I’m curious as to whether all of their controllers/heaters are shoddily made.

By all means!

This sort of thing would be best done as a disassembly to examine construction quality, before reassembling and stress testing to the failure point using progressively higher loads!

See King of DIY (Joey Mullen) via YT and his podcasts with these Hygger heaters.

I have seen these… it’s a bit alarming, to be honest!


In fact, I installed a Hygger automatic pond feeder on a turtle pond not too long ago… it’s all well and good, aside from the power adapter, which stick almost 5” straight out from a power outlet…

This wouldn’t be an issue, except that these devices are more or less exclusively installed outdoors, and plugged into outdoor electrical with an “in use” cover… due to the extreme length of the plug end power adapter, the “in us” outlet cover cannot be closed.

I have reached out directly to Hygger about this issue, to which they responded that the concerns would be escalated, but had no alternative power adapter to offer…

— needless to say, I figured any concerns I brought to their attention regarding this heater controller would be basically ignored… it seemed prudent to instead warn other consumers about these egregious flaws…

 

[Bear22]

By all means!

This sort of thing would be best done as a disassembly to examine construction quality, before reassembling and stress testing to the failure point using progressively higher loads!


I have seen these… it’s a bit alarming, to be honest!


In fact, I installed a Hygger automatic pond feeder on a turtle pond not too long ago… it’s all well and good, aside from the power adapter, which stick almost 5” straight out from a power outlet…

This wouldn’t be an issue, except that these devices are more or less exclusively installed outdoors, and plugged into outdoor electrical with an “in use” cover… due to the extreme length of the plug end power adapter, the “in us” outlet cover cannot be closed.

I have reached out directly to Hygger about this issue, to which they responded that the concerns would be escalated, but had no alternative power adapter to offer…

— needless to say, I figured any concerns I brought to their attention regarding this heater controller would be basically ignored… it seemed prudent to instead warn other consumers about these egregious flaws…

More than just the design flaw(s); it's also Hygger's response to these electronic issues. Joey did a podcast with another aquarist who lost an entire tank of expensive freshwater rays (the animals were electrocuted) and Hygger's "fix it offer" was a $300 dollar check and the signing of a NDA.

Kudos to the guy, he refused their offer and chastised them for their unethical response.

 

[TangerineSpeedo]

All my tanks run Helios. They mostly are amazing when you exclude the higher price tag, more watts per gallon and human error. If there is something that does not line up, the system shuts itself down. Better to have a cool tank than a cooked one...