oven temperature hassles

[Mike Scott]

Hi all. I wouldn't mind an opinion here please.

We bought a new electric oven - a Hotpoint HUE53 - back in July, and
found that it was decidedly on the "slow" side (especially for a fan
oven). I eventually bought an IR thermometer and found the internal
temperature to be anything up to 30-40C lower than the control knob. So
an oven supposedly good for 250C is only reaching perhaps 210-220C.

The vendor, a local company, arranged for a Hotpoint engineer to check
it. He used a probe thermometer, measured I think 220C after 30 minutes
(agreed with my measurement) and declared this was "well within
tolerance" -- although neither the tolerance nor his measurement appear
on his worksheet which I have. (He also spoke a lot of techno-rubbish,
which makes me singularly dubious about his finding.) I've not measured
such a high figure since.

I've just phoned Hotpoint. Their view is I'll be liable for a £54
"no-fault" fee if they send someone else to check and he agrees with the
original engineer. But the guy I spoke with had no idea what any
temperature tolerance might be. Not helpful.

So, back to the vendor I suppose.

Questions:

Does anyone know what the BS figure is for oven temperature tolerance? I
know there is one; I even know the number of the standard (BS EN 60350),
but it's not easy to get sight of a copy. Our local repair shop reckons
this is on the low side.

Presumably if there is a problem, the vendor should sort it; but all
they'll do is get Hotpoint to come out..... so what happens then? Who pays?

If we didn't need a cooker, I'd send it back!!


Thanks. (And I won't be buying another Hotpoint anything. Even the
engineer slated the quality!!)


--
Mike Scott (unet2 <at> [deletethis] scottsonline.org.uk)
Harlow Essex England

[Andy Burns]

Mike Scott wrote:
> Does anyone know what the BS figure is for oven temperature tolerance? I
> know there is one; I even know the number of the standard (BS EN 60350),
> but it's not easy to get sight of a copy. Our local repair shop reckons
> this is on the low side.

Sign up for an online account with Manchester Library (regardless of
where you live) this gives you access to many documents in the British
Standards Online, you have to sign in via the library, which passes
through some form of authentication to the BSI at

<https://bsol.bsigroup.com>

The document you quoted seems more concerned with energy consumption,
than temperature regulation, it does mention +/- 5 degree C calibration
but for the purpose of the energy test, not suggesting the oven must be
capable of that accuracy in normal use.

[Theo Markettos]

Mike Scott <usen...@scottsonline.org.uk.invalid> wrote:
> Does anyone know what the BS figure is for oven temperature tolerance? I
> know there is one; I even know the number of the standard (BS EN 60350),
> but it's not easy to get sight of a copy. Our local repair shop reckons
> this is on the low side.

The standard you want is IEC 60350-1 as modified into EN 60350-1: the BS
version is just a copy of the European Norm enacted into UK law.

I can't find a copy online, but the best I could find is this:
https://webshop.ds.dk/Files/Files/Products/M251203_attachPV.pdf

That gives the differences between the IEC and EN versions. They don't give
temperature tolerances as such, but Annex E has a table to fill out while
testing an appliance and there the target temperature is given as 220+/-10 -
ie within 10 degrees Celsius. That page is 'informative' rather than
'normative' however (ie it isn't law).

It looks like section 7.3 of IEC 60350-1 is what gives accuracy of
temperature control standards, if you can find a way to see it.

Theo

[Ian Jackson]

In article <n19vaq$mkd$1...@dont-email.me>,

Mike Scott <usen...@scottsonline.org.uk.invalid> wrote:
>The vendor, a local company, arranged for a Hotpoint engineer to check
>it. He used a probe thermometer, measured I think 220C after 30 minutes
>(agreed with my measurement) and declared this was "well within
>tolerance" -- although neither the tolerance nor his measurement appear
>on his worksheet which I have.

If you don't have it on the worksheet, I hope you made a note of your
own at the time.

>Does anyone know what the BS figure is for oven temperature tolerance?

I don't think any BS standard is but according to Wikipedia the
difference between 248C and 218C is the difference between gas mark 7
and gas mark 9.

I don't think you should be expected to put up with an oven that is
sold as capable of 250C but can only do 220C. I don't imagine that a
judge would say you should.

(The BS standard might be helpful if it supports you but I don't think
it's critical to your case. It seems like a clear cut case of goods
not as described.)

>Presumably if there is a problem, the vendor should sort it; but all
>they'll do is get Hotpoint to come out..... so what happens then? Who pays?

If you are prepared to go to court, they will pay, eventually.

>If we didn't need a cooker, I'd send it back!!

How long have you had it ? I would definitely be thinking about
sending it back, if I were you.

Depending on how long you've had it, when you told them about the
problem, and so on, you may be entitled to send it back and get a
refund. You can then buy a different oven.

So, what is the history of your purchase and this dispute ?

--
Ian Jackson <ijac...@chiark.greenend.org.uk> These opinions are my own.

If I emailed you from an address @fyvzl.net or @evade.org.uk, that is
a private address which bypasses my fierce spamfilter.

[Tim+]

It's amazed me how difficult it is to get an answer to what should be a
very straightforward question! I can find lots of info on surface
temperature testing and standards but nothing on internal temperature.
Hard to understand why this info should be so elusive.

Tim

[David L. Martel]

Mike,

Is not the thermostat/temp circuit calibratable? Most ovens should be
calibrated after intallation. Never seen this done by installers. It's not
hard but requires some time and an oven thermometer. If this is not covered
in the owners manual then use Google to find out how to do this.
Basically, you punch a few buttons to put it into cal mode, run the oven
with the thermometer, Compare the actual temp with the set temp, do some
math, and adjust the cal setting. Then repeat. It takes a couple of tries to
get it right. Right seems to be +/- 5 deg or so.

Good luck,
Dave M.

[Davey]

On 03 Nov 2015 13:09:29 +0000 (GMT)

ijac...@chiark.greenend.org.uk (Ian Jackson) wrote:

> So, what is the history of your purchase and this dispute ?

He does say he bought it in July, in the OP.

--
Davey.

[Peter Parry]

On Tue, 3 Nov 2015 09:40:47 +0000, Mike Scott
<usen...@scottsonline.org.uk.invalid> wrote:


>Questions:
>
>Does anyone know what the BS figure is for oven temperature tolerance? I
>know there is one; I even know the number of the standard (BS EN 60350),
>but it's not easy to get sight of a copy. Our local repair shop reckons
>this is on the low side.

I used to have a copy of one of the predecessors to the current 2014
version of that standard but as I recall 60350 was concerned with
methods of measuring performance (mainly for energy efficiency rating
and temperature of exposed surfaces) rather than the actual
performance of the oven. I've never seen a definitive document
setting out temperature control accuracy (which given that accuracy
and oven thermostats are rarely found in the same bed together isn't
unexpected).

You may find your local library has access to British standards so you
might be able to look at 60350 there (rather than pay £200+ for a
personal copy!)

>Presumably if there is a problem, the vendor should sort it; but all
>they'll do is get Hotpoint to come out..... so what happens then? Who pays?

Depends upon whether there is a problem. Firstly, measuring oven
temperature with an IR thermometer is prone to significant inaccuracy
unless you know the emissivity of the exact surface you are looking at
and the thermometer is set to that. Also the cooker temperature will
spend most of its time above and below the set point. If you measure
time against temperature the temperature will show a sawtooth, so for
a set temperature of 155deg C the spot readings may be as low as
135deg and as high as 175deg with the average over time being 155deg.
All on/off thermostats behave similarly.

The temperature is normally measured by taking the mean of the
thermostat on and off temperatures after allowing about an hour from
cold for the oven to stabilise. Another method is to put the sensor
probe into a 500ml glass beaker of cooking oil, the mass of the oil
evens out fluctuations in measured temperature.

The calibration accuracy (temperature against dial setting) of a
domestic oven is typically +/ - 10 % at best so for a dial temperature
of 250deg the actual temperature will be somewhere between 225 and
275deg. I've seen anything from +/-10% to +/- 20% quoted as being
acceptable deviations but the most common figure quoted is +/-15% so
that would give you (at a set temperature of 250deg) anything from
212 to 290deg which is within the range you have measured so far.
This sort of variation is pretty universal across cookers regardless
of make (and why all cookery books suggest you buy an oven
thermometer!).

If you were to ask for another check and it was within the limits
above it would be reasonable for the supplier to charge you for the
work. You could then argue in court that you didn't know the cooker
would be inaccurate and you were not told it at the time. However,
given that almost all cookers have much the same characteristics (and
have had since the gas "Regulo controller" in the 1920's) I'm not
sure how successful you would be.

[Peter Parry]

On Tue, 3 Nov 2015 11:38:44 -0000 (UTC), Tim+ <tim.d...@gmail.com>
wrote:

>
>It's amazed me how difficult it is to get an answer to what should be a
>very straightforward question! I can find lots of info on surface
>temperature testing and standards but nothing on internal temperature.
>Hard to understand why this info should be so elusive.

I suspect it is because oven temperatures/controllers have never been
accurate and have never been considered by oven users to be so. Once
upon a time you had 3 compartments in a range - one was hot another
not so hot and a third cool. When gas cookers came along they were no
better until in the 1920's the "New World Regulo thermostatic
controller appeared. Even then with an open burner the range of
temperature within the oven was significant (about 30 to 50 deg
between top and bottom shelves) and the controller pretty hit and
miss. The Regulo dial was never calibrated in degrees (thought to be
too complicated for the servants) but in "Gas Mark" numbers.

Electric ovens showed a smaller temperature gradient and fan ovens
very little. However, all until recently shared the same high
hysterisis on/off temperature switching which allows for significant
temperature excursions around the set point.

Most oven users simply treat the dial as a rough guide and bakers at
least will all mutter whenever they buy a new oven as you have to
"learn" its characteristics.

Given the bang bang thermostat controller allows variations of about
+/- 20 deg around the set point I'm not sure how a manufacturer could
sensibly present this information in a useful way or if many people
would want it. Even with modern electric ovens cooking is still done
essentially on hot, not so hot and cool.

[Ian Jackson]

Oh so he does. Well then I think the `short-term right to reject' has
been lost.

So the OP is entitled to demand repair or replacemement. (Consumer
Rights Act 2015 [1] 19(4), 23, 24.) The OP can perhaps choose whether
they prefer repair or replacement (CRA 23(2), 23(3) etc.)

If the supplier refuses to repair or replace within a reasonable time
then the OP has the right to the reject (24(5)(c)).


So the OP should write a letter to the supplier along these lines:

REPLACEMENT OR REPAIR OF OVEN

On date X I bought oven Y etc. etc. The oven was described as
having a maximum temperature of 250C.

I have found that the oven cooks slowly. On date Z I informed you
that I had measured its maximum temperature as 220C. On date P your
technician visited and measured the temperature. Your technician
confirmed that the maximum temperature was 220C (after 30 minutes)
but told me that this was "within tolerance".

I am not satisfied. An oven advertised as capable of 250C should
not fall short by as much as 30C. This makes a significant
difference to cooking times, and to the quality of the results in
some recipes. I am entitled to an oven that performs substantially
as described; it should be capable of reaching at least 240C after
30 minutes.

Pursuant to section 23 of the the Consumer Rights Act 2015 I require
you to replace or repair the oven. You must do so within a
reasonable time; I will give you 28 days from today.

If you are unable or unwilling to effect a suitable replacement or
repair I will reject the oven. I will then expect a full refund
from you (Consumer Rights Act 2015 section 24). I will then
purchase another oven elsewhere.

I look forward to hearing from you very soon.


[1] http://www.legislation.gov.uk/ukpga/2015/15/part/1/chapter/2/crossheading/what-remedies-are-there-if-statutory-rights-under-a-goods-contract-are-not-met

[steve robinson]

On Tue, 3 Nov 2015 09:40:47 +0000, Mike Scott
<usen...@scottsonline.org.uk.invalid> wrote:

I would be inclined to check the following

1) input voltage of equipment
2) Actual voltage at the cooker feed
3) check cable size
4) Rating of your main electrical input
5) actual operating temperature of the oven

Low input voltage will affect the operation of the oven, UK supply
voltage is nominally still 240 volts although generally now declared
voltage is 230 volts it can however be as high as 253 volts or as low
as 216 and still be considered in tolerance , this could affect the
temperature of your oven dependant on the method temperature is
controlled

Cable size may be an issue too if its undersize the equipment may not
be able to pull its full load

Local supply capacity can make a difference too, in older houses the
incoming cables are not as large.

Put a container of cooking oil in to the oven heat it for half an hour
and check the temperature with an oven thermometer.

The numbers on the dial are often only an indication of approximate
temperature .

Check in the manual for any information .

[kat]

On 03/11/2015 15:21, Peter Parry wrote:
> On Tue, 3 Nov 2015 11:38:44 -0000 (UTC), Tim+ <tim.d...@gmail.com>
> wrote:
>
>>
>> It's amazed me how difficult it is to get an answer to what should be a
>> very straightforward question! I can find lots of info on surface
>> temperature testing and standards but nothing on internal temperature.
>> Hard to understand why this info should be so elusive.
>
> I suspect it is because oven temperatures/controllers have never been
> accurate and have never been considered by oven users to be so. Once
> upon a time you had 3 compartments in a range - one was hot another
> not so hot and a third cool. When gas cookers came along they were no
> better until in the 1920's the "New World Regulo thermostatic
> controller appeared. Even then with an open burner the range of
> temperature within the oven was significant (about 30 to 50 deg
> between top and bottom shelves) and the controller pretty hit and
> miss. The Regulo dial was never calibrated in degrees (thought to be
> too complicated for the servants) but in "Gas Mark" numbers.
>

Last year we bought a new cooker, and the gas ovens are calibrated in
degrees.

--
kat
>^..^<

[Yellow]

In article <n1a6c4$l1j$1...@dont-email.me>, tim.d...@gmail.com says...

As it is not a safety issue, there probably isn't a standard for the
inside temperature - just a manufacturer's promise.

What does the specs section say in the handbook? Does that not give you
a tolerance.

[Peter Parry]

On Tue, 3 Nov 2015 16:52:09 +0000, kat <little...@hotmail.com>
wrote:

You obviously have a better class of servant :-)

[Gordon Henderson]

In article <lnih3bt48qp5od20o...@4ax.com>,

Peter Parry <pe...@wpp.ltd.uk> wrote:

>Electric ovens showed a smaller temperature gradient and fan ovens
>very little. However, all until recently shared the same high
>hysterisis on/off temperature switching which allows for significant
>temperature excursions around the set point.
>
>Most oven users simply treat the dial as a rough guide and bakers at
>least will all mutter whenever they buy a new oven as you have to
>"learn" its characteristics.
>
>Given the bang bang thermostat controller allows variations of about
>+/- 20 deg around the set point I'm not sure how a manufacturer could
>sensibly present this information in a useful way or if many people
>would want it. Even with modern electric ovens cooking is still done
>essentially on hot, not so hot and cool.

All of the above.

I have 3 ovens and they all have bog-standard capillary tube thermostats
and all behave totally differently.

And fan ovens still have hot spots and cool spots (even the expensive
ones - I have one that cost over a grand and the sides are hotter than
the middle of each grid) it's all to do with the design/shape of the
baffles that throw the hot air into the cavity.

I've got some thermocouples in one of my ovens - here's a link:

http://unicorn.drogon.net/beaky2.png

That's cooking a couple of cakes with the dial set to 180°C (the Y axis
is *10) Yellow & red are at the back where the capillary tube is,
blue is at the front..

Gordon
(part-time baker, part time geek)

[Judith]

I think many would want it. I also have been through this process, with no
idea of the +/- range.

"Please note the set temperature will not be absolutely accurate. For example
if you set the required temperature to 220 degrees - then the actual
temperature of the oven may vary between 200 and 240 from time to time. "

[Wm...]

Tue, 3 Nov 2015 17:18:44 <epph3bd5ktof7fi2i...@4ax.com>
steve robinson <st...@colevalleyinteriors.co.uk> wrote...

>Put a container of cooking oil in to the oven heat it for half an hour
>and check the temperature with an oven thermometer.

=== and ===

Tue, 3 Nov 2015 14:47:35 <sr4h3bhvkngid1ekn...@4ax.com>
Peter Parry <pe...@wpp.ltd.uk> wrote...

>The temperature is normally measured by taking the mean of the
>thermostat on and off temperatures after allowing about an hour from
>cold for the oven to stabilise. Another method is to put the sensor
>probe into a 500ml glass beaker of cooking oil, the mass of the oil
>evens out fluctuations in measured temperature.

========

Ummmm, if you try this at home choose your oil and container / beaker
with care.

Many / most common cooking oils are unpleasant at 250 deg C and many
household (as opposed to lab) beakers / containers may not perform as
expected either.

--
Wm...

[Brian Reay]

To get proper controller of a closed loop system, you really need what
is known as a 'three term controller' or PDI controller, Proportional,
Derivative, Integral. These apply the 'thing' giving the change (in this
case the power to the element of the oven) in proportion to the charge
required, the required rate of change (derivative), and the integral of
the error once the target is reached.

Domestic ovens don't have PDIs, they just turn the power to the element
on and off. Depending on the temp. sensor, this may well mean there is
an over shoot. Eg. If the oven is set for 220 and the sensor trips at
220, then as the heater will be fully on until the 'last minute' then
the oven will over shoot the target temperature.

Also, the sensors tend not to turn off and on at the same temperature
(the technical term is hysteresis), which gives a 'dead band'.

In theory, the volume of air, metal case etc. should 'even out' some of
these effects. By how much, I don't know.

[Davey]

On Wed, 4 Nov 2015 09:43:39 +0000
Brian Reay <no...@m.com> wrote:

> To get proper controller of a closed loop system, you really need
> what is known as a 'three term controller' or PDI controller,
> Proportional, Derivative, Integral. These apply the 'thing' giving
> the change (in this case the power to the element of the oven) in
> proportion to the charge required, the required rate of change
> (derivative), and the integral of the error once the target is
> reached.
>
> Domestic ovens don't have PDIs, they just turn the power to the
> element on and off. Depending on the temp. sensor, this may well mean
> there is an over shoot. Eg. If the oven is set for 220 and the sensor
> trips at 220, then as the heater will be fully on until the 'last
> minute' then the oven will over shoot the target temperature.
>
> Also, the sensors tend not to turn off and on at the same temperature
> (the technical term is hysteresis), which gives a 'dead band'.
>
> In theory, the volume of air, metal case etc. should 'even out' some
> of these effects. By how much, I don't know.

In my industry when I worked, this was known as PID Control, but was the
same thing, just rearranging the letters. PID controls were used for
control of ovens for baking painted car bodies, so had huge heat levels
to control. I had lots of practice manually tuning these systems, and
was very good at it, but then the PLC control systems automated it and
wiped out my need for the skill. Oh well, it was good while it lasted.

I can imagine that it would now be simple to include a simple PID
control in a microprocessor-controlled domestic oven, if the
manufacturer wanted to.

--
Davey.

[Vir Campestris]

On 03/11/2015 17:18, steve robinson wrote:
> Low input voltage will affect the operation of the oven, UK supply
> voltage is nominally still 240 volts although generally now declared
> voltage is 230 volts it can however be as high as 253 volts or as low
> as 216 and still be considered in tolerance , this could affect the
> temperature of your oven dependant on the method temperature is
> controlled

This turns out not to be the case.

If the voltage is lower the element will produce less heat, and it will
take the oven more time to reach a temperature at which the thermostat
turns the element off again.

The temperature at which the element turns off will be unaffected.

Andy

[steve robinson]

Its not the heating process that's the issue its how the temperature
is maintained. Newer ovens rely more on electronic wizardry than ever
before. voltage variations will make a difference

[Clive George]

On 08/11/2015 09:04, steve robinson wrote:

> Its not the heating process that's the issue its how the temperature
> is maintained. Newer ovens rely more on electronic wizardry than ever
> before. voltage variations will make a difference

I'm not convinced the control is any more sophisticated than it used to
be. Though if they're using electronic wizardry, it should be less
susceptible to voltage variations, not more.

[Ian Jackson]

In article <SuWdnS2H9dvT8qLL...@brightview.co.uk>,

Clive George <cl...@xxxx-x.fsnet.co.uk> wrote:
>I'm not convinced the control is any more sophisticated than it used to
>be. Though if they're using electronic wizardry, it should be less
>susceptible to voltage variations, not more.

I read that message just after this one from Jon:

>The civilian government's control of the military is a fundamental
>constitutional tenet of pretty much every country in the world
>(apart from the ones which don't have a military, or are outright
>military dictatorships). The military therefore not getting involved
>in politics is a vital part of democratic government.

Maybe rogue generals should be fitted with mind control chips ?