topic Re: Hot ONT Box! in Full Fibre

Hot ONT Box!

KatKaty — Thu, 25 Jun 2026 15:32:24 GMT

We've just had our new full fibre installation and I've noticed that the ONT wall-box seems hot to the touch. Is this normal?

Re: Hot ONT Box!

jab1 — Thu, 25 Jun 2026 15:42:17 GMT

@KatKaty Mine is 'warm' towards the top. Is yoursi in direct sunlight or a warm/hot room?

Re: Hot ONT Box!

KatKaty — Thu, 25 Jun 2026 15:46:43 GMT

It's out of direct sunlight and it's the front that's hot. I rang PlusNet and was told that this is normal because it has a mains supply direct, but that it will cool a little with use...?

Re: Hot ONT Box!

jab1 — Thu, 25 Jun 2026 15:53:58 GMT

As I said, and PN support kind of confirmed, it will be a little warm. How 'hot' do you think it is?

Re: Hot ONT Box!

Dan_the_Van — Thu, 25 Jun 2026 16:39:23 GMT

@KatKaty

Mine does feel warm to touch which is to me is normal. I suspect the maximum operating temperature would be at least up to 40C.

it has a mains supply direct

I question this comment as it has an external power unit, where ac is converted to 12v DC

The ONT it's self would drop 12v DC down to the required voltages to 3.5 or 5 v dc. which would create heat.