Oil-filled radiator - why must it not be turned on and off at the mains?

[Neddie Seagoon]

Folks,

My hobby room has a 1Kw underfloor heating element, connected to a dedicated off-peak circuit. Most of the time this is adequate but during extended cold spells it's really not sufficient for my old bones.

Accordingly, I've just taken delivery of a new oil-filled radiator (DeLonghi V550920) intending to connect it to the off-peak circuit's

3-pin socket - previously used, I believe, for a standalone storage heater - to take advantage of the 2 hour 'boost' available between 12:00 and 14:00.

Unfortunately, when reading through the instructions, I came across this paragraph:

"Caution: In order to avoid a hazard due to inadvertent resetting of the thermal cutout, this appliance must not be supplied through an external switching device such as a timer, or connected to a circuit that is regularly switched on and off by the utility."

In the real world, I'd have thought plenty of people would be turning this sort of device on and off by plugging/unplugging it or using the wall socket's switch - and I can't see how this would be any different from turning it on and off via a timer or an off-peak circuit.

Can anyone help me to understand what's going on here, please? Is there really some material reason why turning the device off and on "at the mains" is a no-no?

Thanks, Peter

[Adrian]

I take it that it's not a very big room? The normal recommendation is

100-200w/m2.

No, it's pretty much the same thing.

Going on the wording, I'd guess that if the thermal cutout trips, power is still required to maintain it tripped until a set period of time expires. If it's switched off, the trip would reset. If it's switched off- and-on, it may well then return to heating before the trip should be reset. Repeat that repeatedly, and there is a very faintly slim chance that it may eventually overheat sufficiently for the oil to ignite, killing every single nun carrying a basket of kittens within a ten mile radius.

Meanwhile, here in the real world and with a modicum of sanity on the part of the user...

[meow2222]

Sounds like a nonissue on the face of it. Its a bit like the handtools that advise using a mask & goggles, even on needlenose pliers.

NT

[Tim Watts]

Sounds like utter and complete c*ck to me.

I have that exact model (3 in fact plus the Dragon) - or at least the one that looks exactly like it from 3 years ago.

I've been remote switching mine for years - socket timer then ZWave without issue.

In fact, unless it has an inbuilt electronic controller (it doesn't) normal right thinking people would expect to do this.

I honestly do not know what they are on about. It has a thermostat and (hopefully) and internal overheat cutout.

Given there is no reset button (at least not externally) I assume it is either a non resettable cutout or self resetting.

If it is self resetting, I fail to see the problem - it will be a thermo-mechanical device, it's not likely to be something that would magically reset when the mains goes away.

In which case it will reset when the heater cools down a bit and power up again anyway.

Unless they've done something very stupid in the design.

[newshound]

+1

[meow2222]

The cutout may be a thermistor. It may only survive so many cycles. If it fails unsafely with the heater overheating, it will overheat. Which in an oil rad is not the end of the world.

NT

[Tim Watts]

It would seem an odd choice.

Personally I would use a manually resettable thermal trip - the user knows it's tripped and will hopefully rememdy the problem (like a coat fell on it).

If it were me, being me, I would also put a thermal fuse set to perhaps

80C as the ultimate and very reliable failsafe.

the OP has me intrigued - I should have the cover off mine and see what's actually in there... Then we can settle this...

Tomorrow if it looks straightforward.

[dennis]

As oil filled rads should cope with having a coat accidently thrown over them without tripping I think more investigation would be needed and a new limit stat probably required. Its the limit stat that keeps the surface from becoming dangerously hot and the thermal fuse that provides backup for if the limit stat fails.

[meow2222]

no, its the choice of heater power versus area that limits surface temp.

Engineers often do what's cheapest, a thermistor is cheaper than a manually resettable bimetal.

NT

[Tim Watts]

Except these are not "cheap" heaters - and I would expect DeLonghi not top be skimping on safety devices, especially ones that cause problems when operating heaters remotely which is waht half the users can be expected to do...

[meow2222]

so what

ah, assumptions

NT

[Neddie Seagoon]

Thanks to everyone for the comforting 'commonsense' replies.

The outcome of your delvings will be most interesting Tim...

Regards Peter

[Tim Watts]

So I don't expect them to be penny pinching with safety devices!

Not really - the rest of the heater has well made components.

[Tim Watts]

OK - enough of the assumption bollocks...

I just took mine apart. Here's the Flickr Album:

Usual bimetallic air stat, switch (it's dual element, each is around 1kW so positions 1 and 2 are the same output power, 3 is both so full power)

Here's the overheat device:

Pressed against the side of the rad with a leaf spring (cover slightly undone, viewed from the side):

And closer:

(silver thing)

and removed, close up for the part number:

Googling finds:

which is a Sensata Klixon[1] Fixed Temperature Thermostat

[1]

Klixon is on the base:

Indeed - that little plastic tab out the back moves - so I guess is the reset button.

Now, there are a number of reset (or not) options.

The weird thing is I read the part number as 1NT08L which is described as "1NT08 Manual Reset / Silver Contacts" which agrees with what I think it should be.

However, the case style is wrong (page 2 PDF)

It looks more like a 1NT02 series - as the terminals come off at 45 degrees.

Can anyone have a look at the photo and check - the "8" is a bit damaged so it might be another digit.

The rest of the code decodes thus:

L - Limit switch (ie NC contacts)

5841 - Customer specific code L180 - Limit, 180 (F or C?? code is missing) MR - Manual Reset 240V@16A max, 10 cycles max

So I think it's reasonable to deduce that it is set to 180 Fahrenheit, and is definitely a manual reset trip which is simple and mechanical (bimetallic disc).

I'm also happy to say I think the construction is good quality and is serviceable - parts are all on spade connectors. Looks like something built to 1970s british standards.

So this brings us back to the original statement re external switching. I am happy to declare, without hesitation "cobblers".

Does anyone wish to add to that, or disagree?

[LumpHammer]

Perhaps some of the manufacturer's fancier models with electronic controls implement some safety features in software? Those might need such a warning in the manual, and perhaps the warning has been copied and pasted into the manuals of other models just in case?

As a minor point, I think the component in your heater is rated at 10000 cycles rather than 10. That's reassuring for me, because the themal cut-out in the poorly designed no-name oil-filled heater I use operates frequently.

[Tim Watts]

It does make you wonder - people often swear manufacturer's instructions are sacrosact - but half the time I wonder if they even proof read them!

Quite right - I see, reading again, it says "X 1000 cycles".

[meow2222]

Its a standard bimetal thermal cutout. I still stand by my position that expecting to not find cheap is naive. Sorry. And delonghi is not a make I hold in high regard. Marketing image means zip.

NT

[Tim Watts]

Could be time to change your view - as I think the construction is pretty solid - but you have the photos, so feel free to make your own judgement.

DeLonghi are the best oil rad maker I have come across todate - can you recommend anyone better?

[Neddie Seagoon]

Tim,

Thanks for taking the time and trouble to post such an interesting and comprehensive reply.

I now feel confident about warming my cockles via off-peak electricity... :)

Regards Peter

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[Uncle Peter]