Hi all. We have a Zanussi single fan oven which came with the house and is approximately 4 years old.
It ovens just fine, but after use the cooling fan (not the main oven fan) continues running and won't switch off even after several hours; it keeps running even after the oven is completely cool. The only remedy is to switch off the power supply to the oven, which loses the clock time.
The model no. is ZOB343X and the production no. is 94406457602.
I was under the impression that the oven cavity temperature is controlled by its own thermostat, and the cooling fan is controlled by a separate thermostat. Looking at the Zanussi website only one thermostat is shown in the exploded diagram, but then two different part numbers are listed for this one thermostat. The accompanying text doesn't help, as it's a generic text along the lines of "thermostats regulate your oven's temperature". One part is a "stirrup thermostat set 140018026165", and the other is an "oven thermostat 3570560056".
Does anyone have any helpful advice on which part I should buy (assuming I can get one delivered)? Obviously I don't want to completely banjax the oven in case we can't get a new one delivered for weeks.
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Well looking at it, it only has one or other, they look different in the way they are fixed in, so you are going to have to pop yours out to see which one it is.
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The main oven thermostat is connected directly to the rear of the control knob (and is entirely different).
The most likely situation is that the oven was fitted with one of two different parts to control the cooling fan.
All the sites I've looked at show two different parts, one marked with a red spot, one with a blue.
As Z says, you're going to have to slip the oven out and check the part (which, afaik, is fitted to the outside rear of the structure).
Given the way it looks like it mounts, the colour of the spot should be easy to see without any further dismantling (as long as it hasn't rubbed/burnt off). Then it is a matter of ordering the matching part.
shop.ukwhitegoods.co.uk/catalogsearch/result/index/?p=2&q=ZOB343X
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Thank you both. Today I've taken the oven out of the kitchen unit and taken off the back and top covers - whilst both thermostats look the same from the back, one does indeed have a red dot and the other a blue dot. Thinking about this, that would equate to hot and cold...
The wiring loom seems to connect all the various components to the circuit board behind the display so there's obviously some electronic control going on, rather than a simple 'stat-controls-fan arrangement. The red dot 'stat connects to the probe inside the oven cavity whilst the blue dot unit is physically closer to the ventilation fan, so I reckon we have our culprit.
I have ordered the blue dot Stirrup thermostat and will report back with the results.
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...that sounds like it's probably a single effective circuit with a "make when hot" thermostatic relay, and a "break when cold" similar.
As it works but doesn't turn off, then the latter would be the suspect, and you'd expect that to be the blue-dot (for cold) one, wouldn't you?
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>> I have ordered the blue dot Stirrup thermostat and will report back with the results.
It arrived today (great work Zanussi!) and I made its installation into a 20-minute electrical engineering lesson for the boys.
It hasn't fixed the problem :/
I don't know whether the cooling fan is supposed to operate from the moment the heating element is switched on; or whether it should only fire up a minute or two into the heating-up period when the temperature of the cavity rises above a preset point. The thermostat I replaced today doesn't have a probe of any sort; it's screwed to the outside of the cooking cavity and measures the temperature of the metal it's screwed to.
I'm beginning to wonder if it's an electronic control unit fault... time to see if there's a relay somewhere.
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>>I don't know whether the cooling fan is supposed to operate from the moment the heating element is switched on
According to the manual it is supposed to operate from the moment the oven begins operating until the oven is cool again.
Page 9, half way down the left hand side.
manualsbrain.com/en/manuals/1588229/?page=9
Last edited by: No FM2R on Tue 31 Mar 20 at 20:05
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>>
>> According to the manual it is supposed to operate from the moment the oven begins
>> operating until the oven is cool again.
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...open to interpretation, but I don't think it says that. I think the switching in and out is automatic, depending on temperature, with overrun if required and controlled by the single thermostat/relay.
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Ah... Thanks. The previous owners didn't leave us the manual and I've only briefly browsed it on my phone before to figure how to set the clock. It looks like I've successfully replaced the overheat protection thermostat then.
The oven maintains its cooking temperature well (in fact it's the most accurate we've owned), so it can't be the main thermostat. Must be a relay or an electronic problem.
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>>It looks like I've successfully replaced the overheat protection thermostat then.
I think so.
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>> It looks like
>> I've successfully replaced the overheat protection thermostat then.
I'm not convinced of that.
In the "whitegoods" page I referenced up thread, the red dot is the safety cutout, the blue dot the fan. (Could be wrong, but the description is clear).
If you turn the whole unit off to stop the fan, once fully cooled down, if you turn it on again does the fan start straight away? I think it should only start once warmed up again.
I'm simply wondering if you've got poor ventilation, and are thus experiencing a very long fan overrun.
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Given the current rating that is generally shown on these units, I'd rather come to the conclusion that they were both thermostatically controlled relays.
I've had reason to revise my thoughts that both would be in the fan circuit, however.
From the descriptions online the red dot one appears to be an oven safety cut-out, which should normally be closed circuit, but will trip (go open circuit) in overheat mode.
The blue dot one is the (only) fan control thermostat/relay, and will be open-circuit when cold, will close as the back of the oven heats up, and then will go open-circuit again once it cools. (off/on/off)
If it works like this (and web research indicates it's likely) then no other control is required.
If you have a meter, you could check for open-circuit when cold via lack of continuity across the terminals (without turning the oven on), or else, but very carefully, remove one of the terminal connections, insulate/isolate it, and try with the oven on. If the fan still runs, there is an issue somewhere else, if it doesn't then it looks like a duff replacement thermostat/relay.
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>> If you have a meter,
I do. Both thermostats showed continuity at room temperature, as does the new one.
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I can't see any reason why the fan thermostat/relay should be anything but NO (normally open) at room temperature. (And I can find online discussion to that effect)
My best guess is that (if it is a *blue* dot replacement) you've got a duff one. Of course we might be mixing up the red and blue, but I've already pointed at a website that says otherwise).
Frankly, I'd be asking Zanussi if it should be NC or NO at room temperature.
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Sit rep: Oven on kitchen floor, back and top removed.
Red dot thermostat was physically looking a bit knackered; the crimped metal lugs holding the block of lightly browned ?ceramic in place were splayed slightly apart allowing it to wobble a little and not make firm contact with the oven cavity outside wall. I've removed the red dot stat and bent the lugs back into their correct position. Upon reassembly I'm still reading continuity across the terminals on both stats.
Fan oven now powered up; I've got an IR thermometer to check temperature against the dial and I'm going to see what happens to the stat resistances at around 100C for starters.
SWMBO in other room, catching up on Eastenders. Child a in bed, child b watching videos of people playing Minecraft in his room.
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I'm now not convinced on the verdict of blue vs red, as I can find conflicting pictures.
I think there is one way to test if you do it safely.
If the blue is the safety cutout (NC), then the oven will fail to work with one terminal disconnected. If it isn't the safety cutout, then the fan won't start.
All caveats about playing with mains electricity apply.
It may well be that you should have replaced the red.
BTW, if there are different amperage ratings on the two, my money's on the higher being the safety cutout.
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Surely the safety cut out should be NC and the cooling fan NO? So if both are closed then it's a matter of working out which is duff. As a rule I'd guess against the new one being duff - not impossible of course, but slightly unlikely.
So I do think you've replaced the wrong one.
You said it overran for hours. Does it overrun forever or just hours? Because if it ever stops then it's working - either the thermostat is too sensitive or as TnE said it's staying too hot for too long.
Wouldn't there be some electrikery whereby the thermostat is open and has no power. When power to the over is switched on then a solenoid is closed which allows the thermostat power. When the thermostat warms and then cools sufficiently I would expect it to switch off the fan and push the solenoid the other way disengaging power from itself.
Surely it can be simply left live?
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>>Surely it can be simply left live?
Surely it cannot be simply left live?
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I've warmed it up to 100C and then further to 140C, the heating element switches in and out perfectly and the cavity temp is within 1degC of the dial setting. So it ain't the main oven thermostat probe.
The cooling fan is still running, and the resistance on the red dot stat hasn't wavered from 0 ohms the whole time. Oven now down to 80C, door open, cheeky bit of tea towel drying in progress.
If the blue dot stat is the overheat protection stat (as it's labelled on the bag in came in...) then the red dot stat MUST be simply the control for the cooling fan. Time to order a red dot stat I reckon.
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>>Time to order a red dot stat I reckon.
Yup.
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I wonder if they'll accept the blue dot one for credit...? I know we don't do so for any electrical parts. I'll give them a ring in the morning. Thanks again for the help, chapter 3 to follow in a couple of days no doubt.
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>> I'll give them a ring in the morning
If you do speak to them ask if there's any logic between the blue and red dots. I'm curious.
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>> If the blue dot stat is the overheat protection stat (as it's labelled on the
>> bag in came in...)
...you didn't tell us that....:-)
The fan relay will get a lot of active use. I suspect that the relay blade has probably welded itself.
I'd stake my left ball (but not both) that replacing the red one fixes it.
(Just pull a terminal off it and see if it stops)
Last edited by: tyrednemotional on Tue 31 Mar 20 at 21:22
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>> >> > If the blue dot stat is the overheat protection stat (as it's labelled on the
>> >> bag in came in...)
>> ...you didn't tell us that....:-)
Yeah, there was no mention of that description on the website or anywhere else I searched for one. I kind of had a sinking feeling when I saw the bag this morning, before I even opened it.
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The wire disconnect whilst running would maybe have been my route to isolating the fault or maybe wiring colouring may have given a clue but then I've not got the thing on my kitchen floor. In any event it has filled some isolation time for those that like to take a stab at fixing stuff :)
Two lots of p&p smarts though.
Who was it that had some problems with their hall light switching a wile back??
Last edited by: Fullchat on Wed 1 Apr 20 at 12:10
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OVEN UPDATE...
I've received and installed the red dot thermostat. The cooling fan now works exactly as it should; that is to say it switches on when the oven cavity rises above about 60C and switches off again when the cavity temperature drops below that level.
This now means we can leave it switched on at the wall and don't have to set the clock (or exit the clock-setting routine) each time we want to cook dinner.
Thanks to Zero, NoFM2R and others for your help and insight. Hope all are keeping well still.
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Result!
...did you manage to return the other one...?
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I've emailed Zanussi but haven't had a response. I've also mentioned as much in both the customer satisfaction surveys I received.
It's not a big issue, if they're anything like my work they're concentrating on fulfilling sales orders and will deal with anything else when they can.
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Well done.
Satisfying for you having fixed the problem and presumably a wife grateful for her husband meddling with things for once.
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Zanussi oven cooling fan runs constantly - Zero
