How do I test NS Oscar element and pressurestat ?

[Azamagnum]

Hi all,

My NS OScar has started tripping the power circuit breaker in the house meter box. Happens a few minutes after turning the machine on, while the thing is warming up.

From what ive read, the problem could be either the pressurestat or the element.

Ive got the top off and can see its innards (power lead unplugged of course). I have a multi meter.

Can someone tell me how I can use my multimeter to test the pressurestat and/or element to see if they are good or faulty ? ?

The pressurestat is the Cimbali brand.
1/4" Pressurestat - Espresso Parts

thanks in advance,
Aaron

[Dimal]

G'day mate...

WRT the Pressurestat, have you had a chance to look through the CoffeeParts catalogue here...
Coffee Parts | Spare Parts for Espresso Coffee Machines - Sirai, Mater and Asso Pressurestats

If you're not sure which item would best suit your machine, contact Pedro at CoffeeParts direct and I'm sure he will be able to help you out. Probably be able to assist with the Element too...

Mal.

[Azamagnum]

Hi Mal,
thanks for reply.
If it is the pressurestat, I will replace it with the same unit, which is the Cimbali one.

I just need some guidance on how to do the testing to determine if its the pressurestat or the element.

I'm over an hour south of Sydney and not sure if there are any good coffee service centres in my area, that's why Im trying to troubleshoot and have a go myself.

Any tips ?

cheers,
Aaron

[coffee_machinist]

It is very very very unlikely to be the pressurestat.

[noidle22]

Pressurestats rarely cause short circuits. If they develop a fault they will either stay closed and keep the element on or not work at all and the machine won't heat.

If it's happening a while after turn on, not straight away, then your element would not be shorted to ground. It would most likely be insulation breakdown of the element.

To test the resistance of the element anyway just to check, disconnect both wires from the element then place the multimeter probes on both terminals. Set your meter to the 200 ohm range, you should see around 48 ohms.
Then, set your meter to the lowest ohm scale then place one probe on an element terminal then the other on a shiny part of the boiler. You should see an open circuit indicated, which means no short to ground.

If you bridge the element terminals with a piece of wire and then conduct the test with the meter on its highest ohm range (above 1M ohm) you should see something around 2M ohm indicated. This is your insulation resistance.
If you see anything below 500K ohm then that's a fair indication of faulty insulation. Generally this test won't work as the resistance test function of your multimeter doesn't apply enough power to the element to cause the insulation to break down.
This is why an insulation tester would be the best tool for this job. It is unlikely that your multimeter has this function, they're generally pretty expensive. My Fluke I use at work is mid spec model, cost about $1500.
What model is your multimeter? Maybe it has an insulation test function, you never know.

[Azamagnum]

Thanks coffee_machinist and noidle22,

I'll do the basic tests on the element as above. Excellent instructions.

Will report back when I get a chance.

In the meantime I will search for the best priced element.

cheers,
Aaron

[Azamagnum]

Thought I should post a follow up now my Oscar is making coffee again.

I used my Mastech multi meter to carry out the tests mentioned above.
"To test the resistance of the element anyway just to check, disconnect both wires from the element then place the multimeter probes on both terminals. Set your meter to the 200 ohm range, you should see around 48 ohms.
Then, set your meter to the lowest ohm scale then place one probe on an element terminal then the other on a shiny part of the boiler. You should see an open circuit indicated, which means no short to ground."

The element seemed to be ok.

Not sure why but I then proceeded to pull the whole machine apart and soaked the tank and associated fittings in a bucket of the descaler fluid.
Everything came up great and I put the machine back together.
I filled the boiler with water thru the water level probe hole in the top of the tank. I did this because I imagined the boiler needs water when its first powered up other wise its trying to heat air ? ? ? Is this called priming the boiler ??

I powered up the machine and a few minutes later the power tripped off at the meter box again.
This time I still had the covers off the machine and was watching for leaky fittings after putting it back together.
I noticed some white crust at the bottom of the pressurestat, and sure enough there was a few drips of water leaking from the pressurestat, where the plastic body joins the metal base.
I assumed it was kaput so I orded a replacement Campini Pressurstat.
I installed it, crossed my fingers and hey presto, the Oscar has made about 10 coffees without tripping the power.

Im not sure how the pressurestat works, or why it tripped the power when leaking water, but the machine seems to be working ok now.

The old black insulation around the tank disintegrated and I bought some stuff from Spotlight. Its called Insul-Fleece. Made by Legacy company I think. I think its very similar to the stuff I saw mentioned on another coffee forum.

I haven't put the insulation on yet. Will do this when I get time.

cheers,
Aaron