Easy Fix For A Vivarium Thermostat that Has Stopped Working

Is your bearded dragon’s vivarium duller and colder than usual? Perhaps the vivarium thermostat has broken. We show you how to possibly fix it cheaply

Easy Fix For A Vivarium Thermostat that Has Stopped Working featured image

3 Steps To Success

About 11 min reading time

Have you woken up this morning to discover that your Bearded Dragon vivarium is looking a little duller than usual? Perhaps you’ve come home from work to discover their tank is sitting at room temperature and the basking light is not working. Do you suspect that your vivarium thermostat might be to blame?

Here’s some things to check before resorting to buying all new equipment. If you think it’s the thermostat that’s broken, you may be in luck – there could be a very simple and cheap fix available. Keep reading for more.

Things To Check

Bear in mind when checking these things that it’s quite possible – indeed highly likely – that there could be two or possible three things that are now wrong. We’ll start with the most obvious first;

Has the Bulb Blown?

This is the most common reason for a cold vivarium. Bulbs normally blow just after they are first switched on. So if your thermostat is an on/off variety, the bulb could blow at any time during the day.

It’s fairly unlikely – unless it’s really obviously broken – that you’ll be able to see whether the bulb has blow or not. The best way to check is to find another bulb that you know is working and try it in the holder. Of course, you need to make sure the fitting is the same. Alternatively, try the suspect bulb in a different holder briefly. Again, needs to be the same kind of fitting though.

If a different bulb works in the vivarium holder then you’re sorted. You’ve found the problem and you can stop looking.

Old bulb doesn’t work in new holder but new bulb also doesn’t work

This is a scenario I just went through, hence this post. The heat lamp had definitely blown in our bearded dragon vivarium – the inside was blackened. But when we replaced it with a brand new bulb, it didn’t work either.

Checking the thermostat I could see that there was no power light showing either. My Habistat Dimming Thermostat has a 3 pin socket to power the basking lamp, so I took the basking lamp plug and plugged it in to the mains directly. Instant heat and light prevailed. So, the bulb was good. But this meant that the thermostat was also now broken.

Fixing a Broken Thermostat

Having discovered that the thermostat itself was also now faulty I suspected that perhaps the fuse in the plug had blown. Sometimes when a light blows it will blow trip switches in the house. In this case all the other sockets were working so I knew it wasn’t the trip switch. Perhaps though it was the fuse in the plug. I changed it. Still darkness.

At this point I thought I was going to be 50 quid down for a new thermostat. We’ve got the Habistat HiRange Dimming Thermostat which we bought in July. It’s been great and we much prefer the dimming aspect compared to the on/off thermostat we previously had. But we were disappointed that it had only lasted 6 months.

Fortunately, I looked a bit harder. Wait – there’s a fuse in the thermostat itself. Perhaps this had blown?

I opened the fuse holder and looked at the fuse. Great, it’s a very non-standard fuse. I’ll have to order one.

On to Google then to find what I need. Fortunately, they’re not as uncommon as they first looked.

In the Habistat Dimming Thermostat it’s a 20mm x 5mm 3.15A 250V Fast Fuse. It’s important to replace the fuse with the same variety to protect your thermostat. There’s various options available on eBay and Amazon that are either the wrong physical size or the wrong rating. There’s others that are slow blow instead of fast blow.

You’ll need the 3.15A 250V Fast Blow 20mm x 5mm ceramic fuse from Amazon. The link to the left will take you to the type that I just bought for mine.

Changing The Fuse

Vivarium Thermostat Showing Fuse Holder

UNPLUG THERMOSTAT FROM THE MAINS. YOU DO NOT WANT TO GET AN ELECTRIC SHOCK FROM THIS THING. It should go without saying, but electric shock from mains AC can result in death. Unplug it first.

Changing a fuse can’t be that hard can it? It shouldn’t be. But the mechanism for the fuse on the Habistat Thermostat is a bit of a nuisance. It’s a strange mechanism.

You’ll need a small screwdriver. To remove the fuse, place the screwdriver into the groove on the top of the fuse assembly. Push the fuse assembly in to the thermostat box. You’ll need to push fairly hard I found. The fuse assembly should go almost flush with the thermostat box. Then gently turn the assembly anti-clockwise about an eighth of a turn. Don’t force the turn. If it won’t turn, you’ll need to push the assembly further into the thermostat body. Once the fuse assembly has turned, release the inward pressure and it should pop out.

Replace the fuse with the same sized and rated fuse. Then the procedure for re-installing the fuse is the opposite of removing.

CAUTION – You Can Break It

I almost did. When attempting to return the fuse to the assembly, if you get it wrong you will bend the metal lugs that hold the fuse in place and provide the conduction surfaces to complete the circuit.

Look inside the fuse holder cylinder on the thermostat. You will see a silver ring at the bottom with 2 lugs sticking out. These lugs are what provide the attachment for the fuse assembly. Make sure the lugs on the fuse assembly are turned a little bit counter-clockwise compared to the lugs in the socket. Then slide the fuse assembly down into the cylinder. You will then need to push the fuse assembly down into the thermostat box. The assembly should go almost flush with the thermostat casing. If you can’t push it in far enough, wiggle it a little and turn it slightly more anti-clockwise until you can get it flush.

Fuse holder metal lugs
Vivarium Thermostat Showing Fuse Holder Metal Lugs

Don’t push down on it all too hard. It’s a little difficult to get in, but it doesn’t require huge force. Too much force will bend the lugs and they’re a nightmare to straighten again. I know….

Once the fuse assembly is flush, turn it approx an eighth of a turn clockwise and release the pressure. The assembly should pop up approx 3-5mm out of the thermostat casing. Try to pull it out gently. If it comes out, you’ve got it wrong 🙂

If successfully changed you can plug the thermostat in and with any luck your basking lamp will now work and you won’t need to replace your thermostat.

The image below should give you an idea how the fuse is inserted and held in place. The very bottom of the fuse holder hole (pictured above) is spring loaded. The picture to the left has an arrow highlighting the mechanism which attaches to the lugs. You can see that the fuse holder will have to pushed into the hole and turned slightly then released.

Fuse Holder showing bent lug
Fuse Holder Showing Lug

The idea being that the attachment sits underneath the lugs and the spring loaded mechanism makes a good contact. I personally think it’s a bit clumsy and too easily damaged, but it is what it is. And it does work – provided you don’t damage it. It’s also relatively safe, since it’s highly unlikely that you’ll get a shock off it

It’s very important for the life of your thermostat device that you replace the fuse with the right rating and fast blow not slow blow. The circuitry inside the thermostat is very sensitive. A sudden current surge from a blowing bulb could be enough to damage the components. A slow blow fuse will not react quick enough to protect the device. Equally, a fuse that has too high rating will not blow early enough and could destroy the device.

Testing The Fuse

If you’re not sure if the fuse has blown there’s a couple of fairly good ways to test it. The easiest way that doesn’t require any extra equipment is to check the ‘Power’ LED on the top of the thermostat. If there’s no power LED lit up (assuming your device has such a thing) then the fuse may well be blown.

Once you’ve got the fuse out you can check it with a multimeter. Set the multimeter to Ohms or Resistance reading and place one probe on each end of the fuse. It should show almost 0 Ohms. You can also set your multimeter to Diode mode (which often includes a beep function). If the fuse is still good then you’ll get a beep when you connect the probes. If it’s blown, you’ll not hear the bleep and your meter will probably display a digit 1.

Hopefully this post saves you having to replace your thermostat quite so often. Blown vivarium bulb is one thing, but replacing the thermostat when a simple fuse has blown is expensive!

If you do discover that you need a new vivarium thermostat then you can find some suggestions on our Equipment Needed For Bearded Dragons page.

Let us know in the comments if you have any questions or suggestions!


  • {node.authorName}'s gravatar
    Toni-LouTuesday, 29th June 2021

    I’m so glad I found this article. Just wish I’d looked online before I attempted to take the fuse out! It says nothing in the paperwork about changing the fuse, so I tried with a screwdriver to open it, but the plastic groove got all chewed up. I had to use a small pair of nose pliers, finally got it out but the metal bits that keep it in place were mashed! Got my new fuse & unfortunately couldn’t get a proper connection, due to the metal bits being out of shape. Tried to straighten them and one snapped off. Luckily I’ve found someone selling spare fuse holders, so I’ve ordered one & now I know how to install it correctly, thanks to your article! Shame Habistat don’t put these instructions in their leaflet. But thank you for taking the time to write this ☺️

    • {node.authorName}'s gravatar
      SteveTuesday, 29th June 2021

      Hi Toni-Lou,
      Thank you for your kind words – we had similar experience and as such thought it was a good idea to let others know 🙂

      Where did you get the new fuse holder from? It would be a good addition to the article too.

      All the very best,
      Steve and Claire

  • {node.authorName}'s gravatar
    Lisa JohnsonWednesday, 23rd June 2021

    Hi can you help me Iv just brought the habitat 600w and once all plug in the heat light and power light come on but when I plug in the heat lamp to the socket the heat light goes off and nothing- it’s a new bulb and works if I plug it into the mains just not if I plug it into the socket connected to the dimming box

    Any advice would be great ful
    Thank you

    • {node.authorName}'s gravatar
      SteveWednesday, 23rd June 2021

      Hi Lisa,
      Thanks for getting in touch. I can’t make out what your particular scenario is I’m afraid. It sounds like the heatlamp works when it’s plugged into the mains but does not work when it’s plugged in to the dimming thermostat? Is the power light going off when you plug the heatlamp in to the thermostat but then comes back on when you unplug the heatlamp?

      I think I’m going to need you to clarify what’s happening, step by step, in order to give a you better idea of what be happening…

      Get back to me and I’ll see what I can do 🙂
      All the best,

  • {node.authorName}'s gravatar
    MeganThursday, 18th March 2021

    Hello I’m wondering if you might be able to help me.. I’ve been having issues with my vivarium at the moment.
    I have a Habistat pulse proportional thermostat, my heater isn’t working properly, the bulb is red hot however no heat is travelling round the viv like normal. I haven’t moved the censor.
    This happened a month ago, I got a new bulb and everything was fine however now it’s happened again, I bought a new bulb but no hope, again it gets hot but no heat travelling. I rang the company (prorep) and they told me it was the actual holder for the bulb that was broken so I went and bought a new one but again no hope.
    Someone told me to test the thermostat with a lamp and to put ice cubes under the censor and then something hot under the censor to make sure it was working correctly, it is!
    I have absolutely no idea what is wrong but I have a Pygmy hedgehog and if I don’t get this fixed soon he could attempt hibernation.. he is already not wanting to move around as much and I’m getting really worried I have no idea what to do and nobody seems to be able to help.

    Any advice is appreciated! Thank you

    • {node.authorName}'s gravatar
      SteveFriday, 19th March 2021

      Hi Megan,
      I can’t give you any specific advice regarding Pygmy hedgehogs as I have no idea at all about them. But I guess I can give you some general ideas perhaps.

      I’m not sure what type of bulb you have for a Pygmy Hedgehog – is it one that illuminates as well as providing heat, or is it just a heat emitter?

      How big is the bulb (how many watts?). How big is the vivarium? Which material is the vivarium made from? Does the vivarium have an open (or mesh) top or is it a closed space?

      The only suggestion I can think of at this stage would be to invest in a Ceramic Heat Emitter for the other end of the vivarium which might help that end. But that would require another thermostat, particularly if your hedgehog requires a warm end and a cool end like Bearded Dragons would.

      Let’s see what the answers to the questions above are and we’ll see if we can come up with some other suggestions 🙂

      Steve and Claire.

  • {node.authorName}'s gravatar
    Karen RawstronTuesday, 23rd June 2020

    Hi….I’ve just read your article on fuses for the habistat dimming thermostat….it’s very good as the same has happened to mine but you suggest a 3.5 amp ceramic fast blow fuse but on the back of the unit is says do not exceed 2.6 amp!! So I’m a bit confused as to which one I should try. Can you help?

    • {node.authorName}'s gravatar
      SteveTuesday, 23rd June 2020

      Hi there,
      It may be that yours isn’t the HiRange version perhaps? Nevertheless, if the device specifies a 2.6amp then definitely go with that instead.

      Hope that helps,
      Steve and Claire

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