Hotpoint Oven turning itself off - diagnosis help please

[Mike Gibbons]

Hi,

I have a Hotpoint AHP662X built in oven with a fault. If anyone can help with the diagnosis I'd be very grateful. Here's what happens:

1. Turn on oven - normal fan setting.
2. Oven warms up normally, thermostat clicks and the heating up light goes off.
3. After a while - 10 to 30 mins - oven goes off entirely. Fan stopped clock display goes off.
4. A few minutes later the power comes back on.
5. Oven works for a while before repeating the cutting out cycle.

I'm happy digging around in the back and I have a multimeter if more information is needed.

Thanks in anticipation- - Mike

[Harry Bloomfield, Esq.]

Mike Gibbons wrote on 31/01/2021 :

Possibly a poor connection which is heating up when on, then going open until it cools down.

Never come across one in an oven, but the alternative could be an over- heat stat, which resets itself when it cools.

[Alan]

The Overheat thermostat or its fan are a likely cause. Has it got a case fan, not for cooking, but to keep the electrics cool? This is normally a

100mm or so fan on the back casing. It is controlled by either a timer pcb, or a stat. If the internal casing overheats the stat cuts all power. Also, on some ovens, the overheat stats for the oven also cut all power. Check the fan first if it has one, then the 2 or 3 stats.

[JohnP]

Someone I know used to turn the cooker off at the mains as the fan running on bothered him - he thought it was a fault! I bet he wasnt the only person to misunderstand the fan.

[Mike Gibbons]

Thanks all - I'll get the oven out in the next day or so and have a dig around

[Nick Odell]

Another diagnostic question I'd ask is: how hot are you setting it and how hot is it actually getting before it cuts out?

My son had a similar problem with a similar oven: the oven thermostat had failed so the thing kept on heating up until the thermal cut-out

-erme- cut out. That took around half an hour from switch-on IIRC.

Nick

[Mike Gibbons]

Hi Nick,

Good point. I have it set to 200 degrees. The main thermostat gives the appearance of working:

Turn oven on - warming up light comes on. Some time later a click sounds and the light goes off. Some time after that another click and the light comes back on.

I'm pretty sure that the oven turns itself off when the warming up light is off.

So could it be that the thermostat isn't working even though it looks like it is so the oven keeps on heating up until the overheat trips?

I need to find a way to measure the oven temperature

Mike

[Clive Arthur]

And try running the oven at a lower temperature - say 100'C - and see if it still cuts out.

[Nick Odell]

I think, as a test, I would try setting the oven to a gentle warming temperature like 60C to 100C and see if the thermostat clicks in and out and the temperature remains low. If the oven temperature just keeps on rising I would conclude that the thermostat is knackered: if the temperature in the oven remains low and the oven still shuts itself down after half an hour then it must be -erme- something else!

Good luck,

Nick

[Nick Odell]

Apologies, Clive. I hadn't seen your post when I wrote exactly the same thing.

Nick

[Mike Gibbons]

Hi,

This morning's test:

1. Set temp to 60 degrees with a thermometer in the oven
2. Oven warms up until thermometer shows 52 degrees. Thermostat clicks off. Temperature stops climbing
3. Temperature drops to 47 degrees. Thermostat clicks back on.
4. Thermostat continues maintaining the temperature at about 50 degrees. Oven remains on - tested for 40 mins - normally would have cut out by then.

My conclusion: main thermostat is behaving correctly (at least at 60 degrees) .

I think the next step is to take a look to see if there is a case fan.

[Mike Gibbons]

This afternoon's test:

1. There is a second fan next to a chimney at the top of the oven - everything looks clean and in good condition. It is connected via a temperature sensor in the chimney. I heated up the sensor with my heat gun and after a minute of so the fan turned on - the oven was not switched on.
2. I turned on the oven at low temperature. Used my heat gun to heat the overtemperature thermal cut-out located next to the element. After a minute or so the oven cut out - exactly the same as the fault I have. It came back on a few seconds after I removed the heat gun.
3. My prognosis a) faulty overtemperature cut out operating at the wrong temp b) something else cutting out when things get hot.
4. Proposed course of action: replace the overtemperature cut-out and go round all the connections I can see to make sure they are secure.

How does that sound? Any other ideas?

Thanks again, Mike

[The Natural Philosopher]

You have reproduced the symptom. You have not identified the cause.

(c) failed man thermostat causing oven to overheat

Start by buying a cheap oven thermometer and seeing if the stat is controlling the oven properly..

[Peter Burke]

Mike Gibbons [e-mail] wrote in news: [e-mail]:

Good analytical method :-)

By all means change the overtemp cutout but I think it an unlikely failure mode.

More likely I think would be an air leak from the inside of the oven to the case. With the oven set high that will leak high temperature air into the case cavity and cause the overhea to trip.

Try an internal visual inspection or feel around for hotspots as the oven heats up.

[Mike Gibbons]

Hi Natural Philosopher,

Thanks for your reply. Further back up the thread I did a test as you described. The main thermostat controlled the oven temperature - I had it set to 60 degrees and it clicked in and out maintaining the temp.

[Mike Gibbons]

Hi Pete - I will check as you describe. Do you know the temperature that an overheat trips? I'm thinking that I'd be smelling things getting very hot (which I am not) if it was tripping at the correct temperature. One other thing when I shake the overheat sensor I can hear it rattling inside - does anyone know if that's normal? Anyway I have a replacement ordered.

[The Natural Philosopher]

Then check that the whole oven has correct ventilation. Its unusual to over temp at normal cooking temps.

I would expect a hot air gun to trip a *normal* overtemp thermostat

*easily*. they are HOT.

[The Natural Philosopher]

Probably in the 100°C-200°C range. Its there to stop stuff catching fire

If its cheap and easy, its the next thing to do

[Mike Gibbons]

Hi all,

I think I'm ready to declare victory on this one. I did as planned - replaced the overheat sensor (£15 ebay) and wiggled all the connectors I could find. The oven has functioned correctly over three days now. Many thanks to all who contributed from my favourite forum! Mike

[Peter Burke]

Mike Gibbons [e-mail] wrote in news: [e-mail]:

Glad you're sorted and thanks for feeding back, I hadn't seen that low temp trigger failure mode before.