Bosch Exxcel W/ Machine Heater Problem

Aye edd, anyone would be forgiven for assuming it was virtually impossible that two brand new parts would be faulty.

oh I see. So both replacements had no current going through them. Yes that is very bizarre indeed unless the place they were purchases from were very rough handlers of goods.

Hi Edd, Lolly is saying the heating elements were open circuit. The original element was definitely "knackered", but two replacements were open circuit, a third one was OK. It's definitely bizarre and something you would't expect to happen.

I'm confused.com ??? If the thermostat is built into the heater element then I fully understand. If not, then how could it be the element??? It's a switched device by the thermostat (depending on selected temperature). So if the temperature is set to say 80, then the element will turn on and not go off until that temperature is reached. Once the temperature is reached, then it switches the element off. Surely the element can't be the fault?

Good news, and it goes to show how fault diagnosis is all about keeping totally logical thoughts and not assuming anything

New heater arrived, fitted and its been perfectly working for a week now.

So the outcome was I was sent 2 faulty heaters!

These were Bosch genuine parts and all three were stamped and looked identical

Many thanks to everyone esp Mr Admin

I checked and the element has 230 volts stamped on it

A new one is ordered from a different supplier and I will meter it beforehand!

Will keep everyone posted

Have you been given 110 volt elements by mistake as these would blow when 230 volts applied ?

'

Acestu

As you can imagine it's not ideal to be trying to diagnose things without being there but I've never heard of a fault that can cause 2 new elements to go open circuit immediately after fitting. If you order a new one test it straight away.. It's definitely a good one this.

Hi I checked the element and it has very slight discolouration so I think you may be right about not overheating

I decided to check the voltage in another way after you said about the wiring

I hooked a light bulb up instead of my DIGITAL meter

After about ten minutes into the programme it lit and didn't light as soon as I Turned the switch etc

Do you think I have just been sold 2 faulty Elements !

Its looking that way to me

Having said that, if it was switched on the live side and had a constant live feed then it would be energised all the time. However this would cause the heating element to warp. If you can imagine putting the kettle on with no water what would happen to the heating element it? It would glow red hot, completely overheat, warp completely out of shape and go very discoloured.

Therefore you need to remove the heating element, if it looks perfectly okay it has not been running all the time.

No, not if it was switched on the neutral side by design. Electricity can flow through any part all the way through and right back to the wall socket, but if there is no neutral available at the wall socket nothing will actually run. Any electrical component can be switched on and off either on the live side or the neutral side.

Most electrical components are switched on and off using the live side. They have a complete neutral return all of the time so as soon as any power is applied to the part it flows all the way through the part, down to neutral and works. If switched on the neutral side then power is always present but it cannot flow through to the neutral supply and make the actual circuit unless it is switched on by a switch on the neutral side.

If the heater relay was stuck it should generate an error. Send the board to QER repairs for testing and repair.

Just metered all of the relays and they seem fine so back to the drawing board

Anyone know of a good source for used boards as I think the problem is somewhere on the board?

I can tell u wat the problem is. Its a bosch! Made in poland

Hi,

Your friend is probably right, if you can get hold of a wiring diagram it should show you any thermostats and relays connected to the heater.

Acestu

Again thanks for the reply

If the heater was powered all the time regardless of any water being present wouldn't it over heat and go open/short circuit?

A friends theory is that when the original heating element went short circuit it drew so much current it melted the relay contacts together.

So now the power is permanently on the heater element unable to be switched by the relay

It is possible that the heating element is switched on the neutral side. Some appliances just have a live feed to virtually everything but nothing will run unless it has neutral return. A fault causing the heater to be powered on all the time wouldn't explain the two new ones going faulty though..

I have done some more testing

I hooked up the meter to the heater element and switched the machine on at the mains

As soon as I turned the dial I got 235 volts on the meter - before actually selecting any programme

I selected mixed load and the voltage was on the heater from the beginning until I stopped the cycle after 15 mins

I then put it on drain and still volts on the heater all the time

It seems there is power to the heater all the time and I suppose this would eventually cause my problem?

Or it did cross my mind the power is on the heater permanently because it's open circuit maybe?

Yes it's quite bizarre. I think you can be forgiven for not testing the first new element. It's perfectly rational to just assume it is okay because it's brand-new. Even as an engineer I would never dream of testing a new element to make sure it was okay I would just assume it is okay and fit it.

You can even be forgiven for not testing the 2nd one because even if you thought the first one might been faulty because the chances of a 2nd one being the same are extremely low. However, we both agree a 3rd one definitely needs testing first :-)

I hadn't realised that the first one was short-circuit so that at least means there aren't 3 open circuit elements. As I said before I can't think of anything that could cause 2 brand-new elements to become open circuit immediately. The only logical thing you can do now is try a 3rd one.

If the 3rd one tests out okay and gives a reasonable reading before fitting, and the machine then works all right I think it's fair to assume the other 2 were faulty and hopefully you can pursue an exchange.

On the other hand if the 3rd one tests out okay but goes open circuit after fitting there is something seriously amiss which needs proper investigation.

If the 3rd one tests out open circuit when it arrives you need to get onto the supplier straightaway. Please keep us informed how this one turns out.

Firstly thanks for the reply I really appreciate it.

Just checked the meter on a known value resistor and its good.

The first original heating element was short circuit just to confirm, the two new ones both were (possibly became) open circuit.

I think I need to exchange the element again and make sure I meter it prior to fitting!

Just had a thought could the thermostat next to the heater be faulty and cause the heater to get way too hot and cause an open circuit?