Bosch Oven HBA64B251B trips the electrics out

[smcuk]

Sunday's roast pork dinner was cooking nicely then suddenly BANG all the lights went out. Soon realised the problem was the oven itself. Switched the oven off and reset the mains RCD and all Ok. Then switched the oven back on and it all lights up ok, reset the clock and then turn the dial and select a temperature...it then takes about a second or two before the oven powers up and immediately the mains is tripped again....investigation required.

After a bit of reading it seems highly likely this is due to a bad element so out comes the oven and off with the back cover. There are three elements on this model, The top, bottom and fan elements. The spade end connections of all three are visible and therefor it is possible to disconnect the spade ends and use a multimeter set on Ohms across each of them. On the face of it all three elements were giving a reading and none appear to be open circuit...

I then tried the following : -

1. Disconnect all connections to the fan element and try powering up the oven again, this resulted in exactly the same mains trip, so reconnect.

2. Disconnect the top element and power up resulting in the same mains trip again, so reconnect.

3. Disconnect the bottom element and power up...this time the oven fired up as normal and all seemed to be working correctly...until I switched the oven off and this then causes the mains to trip also....

I now have no logical path forward unless switching off the oven with the bottom element wires disconnected will always trigger a trip fault, however installing a new bottom element and connecting it up correctly will not cause the trip on switching off...which all sounds unlikely.

Can I ask if anyone has ever experienced anything similar or can think of another idea..?

Cheers

 

[Mr diy a lot.]

Before you mentioned it being the element, my instincts went with element too. It’s a very common part to fail and it’s easy to repair. I would be inclined to gamble and throw £25 at a new bottom oven element and see if that fixes it.
If it does not and there are no other obvious reasons, then it’s time to weigh up whether you could end up throwing good money after bad and a replacement oven could be cheaper.

 

[ericmark]

An insulation tester uses 250, 500 or 1000 volts, multi-meter possibly 9 volt, so multimeter no good for this job.

Elements in the main are mineral insulated, which is hygroscopic that is a substance tending to absorb moisture from the air. So if the seal is damaged they absorb water and need replacing.

To test remember also need to disconnect neutral as still can have a neutral earth fault.

Also since the Oven draws a lot of current it could be a neutral earth fault on any other bit of equipment connected to the same RCD. So even an out side light with water in it could cause RCD to trip as the oven loads up the circuit.

 

[FrodoOne]

Sunday's roast pork dinner was cooking nicely then suddenly BANG all the lights went out. Soon realised the problem was the oven itself. Switched the oven off and reset the mains RCD and all Ok.

Apart from your other problem, you have ONE RCD providing Earth_Leakage "protection" on both the Oven, the lights and who knows what else!
As you now know, this is not a good idea.

I strongly suggest that you replace the RCD and the associated MCBs with RCBOs, so that only the circuit on which any future Earth-Leakage fault occurs is the only one to be disconnected.

 

[SUNRAY]

Apart from your other problem, you have ONE RCD providing Earth_Leakage "protection" on both the Oven, the lights and who knows what else!
As you now know, this is not a good idea.

I strongly suggest that you replace the RCD and the associated MCBs with RCBOs, so that only the circuit on which any future Earth-Leakage fault occurs is the only one to be disconnected.

Although there is some good thought behind the post there is the only priority... Fixing the fault.

 

[FrodoOne]

Although there is some good thought behind the post there is the only priority... Fixing the fault.

OK.
However, you should then fix the other problem !!

 

[smcuk]

I am only hearing the haunting phrase of "...throwing good money after bad..."

New hideously expensive oven just ordered....well someone has to stimulate the economy...

 

[Mr diy a lot.]

Now you have bought a new oven you have bought time to look at old one. You should still try to fix it and if you are successful you might still hear £150 for it on gumtree which can go toward your new one. And you can post your success or lack of it here for hundreds of other people to benefit from in the future!

 

[smcuk]

"..They think its all over..."

What happens when the new oven arrives tomorrow and the electricity is still being tripped out....
Keep 'em peeled on gumtree.

 

[smcuk]

Manage to blag a £100 discount off my new Miele oven which arrived today. Installed it and all is working perfectly.

Poor old replaced Bosch oven looks sorry for itself sitting there upside down where I extracted the bottom element just to have a look at it. The replacement element costs around £90 and then there is still the nagging doubt as to why it was still tripping the mains without the bottom element connected which is enough to say cut my losses and heave it off to the the dump...

Fair point about upgrading the MCB's so the individual circuit should trip before the mains RCD. I think there was a regulation on the house to have a hyper sensitive RCD on the mains because it has a thatched roof. It used to trip out every time there was a thunderstorm in the area.

Thanks to all