Electric hob temp control issue

[mr. shr]

Hi All,

Tenant complained that ceramic hobs were only outputting max temp. regardless of knob setting.
So I’ve replaced the swtiches for 2 of the hobs just to see if that sorts the problem.
Tenant now claims that hob temp does vary between low, medium and high but nothing in-between. i.e. knob positions 1, 4 and 8 correspond to low, med and high respectively. But the other knob positions have no effect.

Is there something else that needs to be tested/ replaced or is this just as good as it gets?

[electrofix]

what is the hob make and model and what switch did you replace ?

Dave

[mr. shr]

Morning,
I replaced the energy regulator/simerstat (MP-V01-SVM) for two of the hobs.
It’s a Belling 444447146 if that helps?

[electrofix]

ok yes that helps

a simmerstat works by changing the time interval the element is on and off. at the highest its on all the time and at the lowest its off. Half way it switches on for half the time and off for half.
if you had got a wiring error it would not work correctly anywhere. when i test them i switch it to no 1 and you hear the plate come on and go off very quickly. there is then a long time interval and it does it again. Raise it to no 2 and the on time increases and the off time decreases

so you can go back and with a stop watch you can tell if it changes the setting as you raise and lower the knob. You can hear the clicks as the simmerstat goes in and out in a quiet room

Dave

[mr. shr]

Thanks that’s really useful. I will go back and try, as you say, with a stopwatch.
But if it doesn’t operate in the manor you described above, what else could it be? There isn’t a control board for the cooker, it’s simply the energy regulator that enables the varying of temp. Is there anything else I should also be looking at?

I still have the two switches that I removed from the cooker. Is there a test I can do on them to see if the are indeed faulty?

[electrofix]

you can only test the switches on main so it would mean messing with mains wiring

it can only be the regulator. and you have fitted 2 of them. as long as you wired it correctly then its unlikely to be 2 faulty ones

have had jobs before where the appliance is ok and the tenant is faulty

Dave

[mr. shr]

electrofix wrote:you can only test the switches on main so it would mean messing with mains wiring [/QUOUE]

If there are some specific tests to do, I’d be willing to do them. I’m an electrical engineer so feel I’m competent.

have had jobs before where the appliance is ok and the tenant is faulty

I’m trying to not be that kind of landlord but to be honest, I think you have hit the nail bang on the head!!

[electrofix]

well you can start with a resistance test

inside these units is a little heater wrapped around a bi metal strip. when you turn the control on the contact closes but the heater is energised so as it heats up it bends the strip until it switches both the ring and itself off. Heater cools and switches back on and the process continues

on the later ones live and neutral are normally P1 and P2. put you meter across and see if you can find the heater resistance. its going to be a fairly high reading as its a low power heater but it has to be under 30K as thats 2 watts and it has to be more than that. dont forget to turn knob to the on position

Dave

[mr. shr]

electrofix wrote:well you can start with a resistance test

inside these units is a little heater wrapped around a bi metal strip. when you turn the control on the contact closes but the heater is energised so as it heats up it bends the strip until it switches both the ring and itself off. Heater cools and switches back on and the process continues

So the temperature of the hob is controlled entirely by the little heater inside the switch, yes?
You mention doing a resistance test, but surely not with the circuit energised. I’d have to switch it on for a few mins, listen for the bi-metalic click, then quickly isolate and disconnect the cables in order to do a resistance test?

on the later ones live and neutral are normally P1 and P2. put you meter across and see if you can find the heater resistance. its going to be a fairly high reading as its a low power heater but it has to be under 30K as thats 2 watts and it has to be more than that. dont forget to turn knob to the on position

Dave

I just tried this on the two switches I removed. They are both giving a vey high resistance (mega ohms) so clearly failed.

I’m wondering if I get a couple more switches from a different supplier to see if that works better? Just to eliminate the question of whether the new switches are also faulty.

[electrofix]

mr. shr wrote:

So the temperature of the hob is controlled entirely by the little heater inside the switch, yes?
You mention doing a resistance test, but surely not with the circuit energised. I’d have to switch it on for a few mins, listen for the bi-metalic click, then quickly isolate and disconnect the cables in order to do a resistance test?

.

yes the ring is either on or off and since it has thermal inertia you can effectivly pulse the power on and off at varing times to get the heat desired

one switch could be faulty but 2 is highly unlikely

Dave

[mr. shr]

I agree, but I need to be doing something.
I’ll try the stopwatch thing and try replacing the other two regulators to see if they are any better.

If not, then don’t really know my next step.

[mr. shr]

OK I’ve been back and now all for hobs have had a new energy regulator fitted. I’m confident that each hob is functioning correctly. I can hear and feel the bi-metal switch click in and out during operation.
Tenant says that when they turn the knob down from, say 5 to 2, the hob is still hot. I’ve patiently tried to explain that electric hobs don’t cool down immediately.
Tenant still not happy but I just don’t see what else there is to do.

[electrofix]

you seem to have a tenant who has been born without common sense.
would they expect a kettle to cool down the minute it gets switched off or their bath to be full of cold water 10 mins after running it. I think not

so where their logic is for this one is beyond me. the only type of hob that cools almost instantly is induction and am sure your not going to fit one just because they have an inability to think

Dave

[mr. shr]

I know. It’s been frustrating.
They’ve accepted that I’ve now done all I’m going to do. Hopefully that’s the end of it.

Thanks for your support with this.

[Author]

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