Moffat Oven

Navy · 19 Apr 2014

I have a old(ish) Moffat oven. It's very basic in that it has just the Selector knob Timer and Temp knob. The oven is seldom used, the last time was probably 4 years ago.

When I came home today the single and only neon on/off light was flickering even though the oven was off. I turned the Temp dial up and the light went off. However, when I turn everything off the light is on Full no flickering.

The oven still works but the neon light is on when the oven is off and off when the oven is on.

So, with the Temp dial turned up and the Selector Knob off the light goes out.

I appreciate this reads confusing but I am hoping someone may have a idea what the problem is.

I have removed the oven from the housing and tried a different socket but the same thing is happening.

Many thanks

Burnerman · 20 Apr 2014

Desperately trying to revive the memory cell on this one.....
Neon indicators are able to energise with induced current and I believe the neon gas inside the bulb starts to energise at around 50v, reaching full brightness at around 80v. A series resistor prevents excess current passing through the indicator. If this fails the after effect is to make the indicator more sensitive to induction current, hence the apparent misbehaviour with your oven.....the lamp is acting upon induction currents within the appliance.
I guess replacing the indicator for a new Maplins one would cause normal operation!
All I've said here may be the usual cobblers, of course

My studies were many years ago!
John

Navy · 21 Apr 2014

Many Thanks Burnerman,

Thanks again for replying. I know that neon indicators act weird after many years as I also have a Vailiant sine 18 boiler which also flickers.

So, I was going to replace the neon indicator as a first step but was unsure if I was overlooking something??

Should I also replace the series resistor you mentioned????
Photos will be available tomorrow as I have booked a day off work

I am happy to try anything with no stings attached!!!!!

Thanks Again

Burnerman · 21 Apr 2014

If the oven and everything is working as it should, just replace the neon......the series resistor is incorporated in the bulb unit.
Maplins have a range of colours - well, three maybe - and they fit in a pre drilled hole. The connections are usually the spade push on type.
John

Navy · 24 Apr 2014

Sorry for the delay in replying.

I bought the neon indicator from Maplins yesterday and fitted it today.

Unfortunately I still have the same problem.

I've added a photo to show the inside of the oven.

So here's what I did. I followed one wire from the neon indicator back to the Mode Selector ( white wire ) then followed the next wire on the double spade connector ( orange ) back to the mains.

The other wire from the neon indicator goes to the thermostat ( currently disconnected in photo ) and the blue wire on the double spade connector back towards the top element and then to the bottom element.

There is 240v across both white wires at the neon indicator.

I have looked at Electrolux spares website and they show different neon indicators ( including the spade type and non spade type ) at differerent prices. I can only assume the non spade type ( which I have ) is different to the Maplins one which is why it's not working. Maybe the resistor is a different (higher value ) or something else is faulty, although everything is working fine with the oven.
View media item 76448Any thoughts would be appreciated as always.

Many thanks

Burnerman · 24 Apr 2014

I think this has to mean that there's a component within the oven that has had a change in resistance....for example one of the heating elements or even the light bulb inside.
Are you still getting 240v across the neon with the oven off? Maybe the main selector switch has an arc across its internal connectors allowing a small current to pass.
Most bizarre!
John

Navy · 24 Apr 2014

Thanks for replying.

With the selectors in off position the light is on and Yes I am getting 240v across the terminals.

I noticed that when I disconnected the blue wire to the top heating element the light goes out.

This blue wire is coupled with the white wire leading to the neon indicator.

I also noticed that turning the mode selector from top element to grill the neon light flickes on for just a second. On closer inspection the top element seems to be two units in one. I think the entire element heats up when selected or only half the element heats up when Grill is selected.

I know its weird as everthing is working perfectly apart from the light.

I removed the selector unit and had a good look underneath. Even though it seems basic the workings are obvious and there is no arcing anywhere.

I used my multimeter and checked for voltages on the left side of the mode selector and everying is dead when in the off position. Which is what I expected.

I diconnected the wire from the thermostat to rule that out too.
So its just the upper element that when disconnected the light goes out.

Thanks again for all your help

Burnerman · 24 Apr 2014

I can't see all of the wiring, but is that neon connected in series with the top element?
My head is in a bit of a whirl here! Maybe you need a meter such as a Megger to see if there is any cross connection somewhere.
Whats your diagnosis?
John

Navy · 24 Apr 2014

Thanks again,

It looks to me that that neon indicator is wired in series to the top element.

I think the megger meter may be a step too far for me as my prognosis involves a landfill

Top elements run at about £35.00 + P&P and £10.50 + P&P for genuine parts.

Since I haven't used the oven or grill in 2 years I may be tempted to change the neon for an original one as my final punt.

I really don't know tbh.

I'll tinker around with it again tomorrow.

I'll be sure to let you know the outcome.

Cheers for all your time helping me though!

Thanks again

captaincaveman1 · 24 Apr 2014

It will be low insulation on one of the elements for sure . If a heating element is not used over time and you state you've not used it for two years it starts to absorb moisture from the air which in turn lower's its resistance to earth. I've been to many customers over the years that have bought a cooker that's showroom ex display installed it and it's tripped the electric's or has caused the "ghosting" of the neon's all because the elements had absorbed moisture whilst it was sitting in the shop's showroom over a long period of time.

Burnerman · 25 Apr 2014

Yep, I think you're on the right track here!
I've found similar symptoms before - but they have always corrected themselves for me after a few heatings / coolings.
John

Navy · 25 Apr 2014

Many thanks to Bunerman and Captaincaveman1 for all the helpful advice. I have decided to buy the upper element today and hope for the best.

Do you think the ohms readings reflect a failing element. I only ask as the bottom element may also be on the way out.

I set my multimeter to 200k and these are the readings

Upper/outer element 63.3 ohms
Upper/inner element 31.7 ohms

Lower element 50.4 ohms

If I need to then I will order both and save on the postage.

Thanks again to you both for helping me

Burnerman · 25 Apr 2014

Those readings sound about right, but leakage can occur which can't be read with an ordinary meter......hence the Megger idea. Its the same sort of thing thats used when PAT testing.
If you went ahead then you'd have an oven that was as new, but all the elements could have the same issue, I guess.
John

Navy · 25 Apr 2014

I was thinking the same thing Burnerman. I'll go ahead and order the lower element too and hopefully that will be that.

I will keep you posted once the parts are fitted.

Many many thanks again

Navy · 12 May 2014

OK.

I,ve had the world of problems with Electrolux ordering parts online.

Anyway, fitted the new top element and hey presto the neon light is off ( finally ) .

Replaced the bottom one also ( suppose I didn't need to ) to be sure.

So, I am grateful to Bunerman and CaptainCaveman1 for sticking with me and helping to find a solution. Very educational for the future and as always I am most grateful for your time spent helping me.

Think I'll buy a megger tester just in case

any suggestions on model?

Thanks again

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Moffat Oven

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