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Evening all, I’ve had a fault recently with a hotpoint free standing electric cooker and wondering if anyone has had a similar problem.

The problem itself is with the induction hob part of the cooker, the hob had blown when a pot was placed on top and the mcb tripped Within a few minutes. The mcb was reset and the hob part of the cooker would no longer work but the cooker section was still was functional.

After having a like for like cooker installed a month or so later the same thing has happened with the same pot which had not been used since the last fault.
 
Is it an especially heavy pot? Its maybe pressed down too hard on the induction plate and made 2 parts touch that aren't supposed to.

Shot in the dark, mate.


I did have a look at a Zanussi induction hob. It came up with an error code. Apparently if the pan is too wide or too narrow a diameter, the induction plate senses it and doesn't come on.
 
Supposedly the second time the pot was almost empty.

The mind boggles tho, two cookers same fault 6/7months in between only correlation between the two is the pot used.


Client is looking into a zanussi cooker as a replacement as it goes.
 
Did you/the client note down any error codes? What was this pot made of - copper and aluminium are unsuitable for basic induction hobs. What is the rating of the mcb and the maximum power requirement of the hob from the rating plate?
 
Did you/the client note down any error codes? What was this pot made of - copper and aluminium are unsuitable for basic induction hobs. What is the rating of the mcb and the maximum power requirement of the hob from the rating plate?

What would be the effect of using the wrong pot? I had a quick read when this thread was posted and noted that copper and aluminium can be used but they need different frequencies? to work.

Would they result in too much power being consumed by the coils, and hence causing damage to the controls?
 
The basic high frequency (20kHz - ish) induction hob is designed to work with magnetic metals like cast iron and some steels. The principle of induction heating is create eddy currents in the surface boundary layer of the bottom of the pan/pot. These eddy currents, are the free electrons of a metal flowing through the surface resistance (ie the resistance of the boundary layer not the bulk of the base of the metal bottom) create Ohmic heating according to Isquared R. The problem in using copper or aluminium is that they are better conductors than iron or steel which means that their surface resistance is lower - thus the Ohmic heating is less from Isquared R. Also, cast iron and some steels, being paramagnetic - which means they do not readily maintain their magentic polarisation but the bound (as opposed to free) electrons do tend to align their spin axes with the applied HF magnetic field. As the applied HF magnetic field is alternating they suffer hysteresis - which creates heat too. To be able to use copper or aluminium one has to use higher frequencies which will produce thinner boundary layers and this effectively a higher skin/surface resistance.

So, what I think has happened is the HF oscillator has been mismatched to its load - it expects to drive a higher impedance load than the pot/pan in question provides - and thus as you say more of the power generated by the oscillator is dissipated in the hob coil and power electronics because the HF current on the primary side of this transformer system is higher than it is designed for. Effectively - think Thevenin equivalent circuit of the primary side of the induction transformer - the lower Zload causes a high current I through the source impedance Zsourse - which does not do it (the HF source ) any good - the Ohmic heating of the resistive part of Zsource is higher. My great surprise in all this is that this problem is highly likely so I would expect some clever electronics to detect it and shut down the HF before irreparable damage occurs - hence the question about fault codes.
 
What’s the max load of the hob? Just wondering how they compare to the power ratings on traditional hob electric / halogen elements? I’m about to install a Neff induction hob rated at 7.4kw
How long had your appliance been installed before it went wrong? Is it on a preecisting cooket circuit? Do you no the cable size and MCB rating?
Only problems I had is with the glass tops breaking but they are fairly easy to replace ....at a cost for the spare part.
 
http://docs.hotpoint.eu/_doc/F085253_HUI612_P_MANUAL.pdf

Do you know for certain that the motherboard has failed? What evidence apart from the none of the hobs or controls work?

I did a quick google of reviews of this freestanding hob/oven and they were good. It makes me wonder if the controls are locked or the hob needs a reset after power up.

And it would be very helpful to know what size mcb supplies the oven and hob - you have not mentioned this yet. We need to know because the hob peak power could be 7.2kW and the oven about 2kW making a total of 9ish kW. (Of interest - the peak power of the induction hob can be reduced - see page 10 Setting the Power Management:

The cooktop maximum power limit is 7200W. This power limit can be reduced by the user to 2800W, 3500W or 6000W.


Is it the cooker in the reference above? If it is then after power is applied or restored the controls might locked. See page 10 'switching on the hob'. If this restores functionality the hob needs to carry out an ambient light calibration - see page 10 'Initial Light Conditions' - if there is too much ambient light this calibration process can fail until the ambient light is reduced. On page 11 it mentions the 'Control Panel Lock' feature - how to activate and de-activate it. It says:

All the keys on the cooking zone selection wil be locked if :the cooktop is off,, if the Control Panel Lock is activated or if an error on a cooktop occurs..

On page 12 on 'Switching off the hob':

Press the button to switch off the appliance - do not rely solely on the pan sensor. If the control panel lock has been activated, the controls will continue to be locked even after the hob is switched on again. In order to switch the hob on again, you must first remove the lock function.

and on Overheating protection:

If the electronic elements overheat, the number signalizing the power level starts flashing, and the letter “c” appears on the display. When the temperature has reached a suitable level, this message disappears and the hob may be used again.

Finally Hotpoint advise on Errors and Alarms:

When an error is detected, the whole appliance or the heater/s are switched off,
a beep sounds (only if one or more heaters are active) and all displays show a ‘F’ letter and the error code (an index number or a letter) alternately. If the problem does not disappear by itself, please contact the Technical Service.

Hotpoint Service We are the largest service team in the country offering you access to 400 skilled telephone advisors and 1100 fully qualified engineers on call to ensure you receive fast, reliable, local service. UK: 08448 224 224
 
11.2kw , 6mm twin 40amp mcb.

There engineer came over today -
they seem to come to the conclusion that it had to be the saucepan even though that seemed weird that it blew the hob rather than just not functioning. He’d never heard of anything like that happening before....

And they will be replacing the cooker for a third time.

Definitely not an over load as only one ring was being used at the time.
 
Would you know what the offending pan was made of or its make/brand/model?

This is not directed at the OP - I still remain surprised that none of the safety features protected the electronics and prevented an over-current of such magnitude it tripped the 40A mcb. My staff would have been expected to go away and delve further - repair by total replacement on two occasions now after using one particular pan - demands further explanation.

What is the mains voltage at the cooker off load and when the conventional oven is on? Have they checked the RFI filter? Are there any internal thermal fuses? Is their adequate ventilation around the oven? Are the vents blocked off? Does the induction hob cooling fan run at the required speed? Have L and N been reversed? Is it earthed? What is so special about the pan?

I/we will never know.
 

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