Hi all,

 

I've got a 6 year old La Pavoni Bar T 2 group machine that has run great since getting it new.  Two weeks ago I found that I had no pressure due to a worn out pressure switch.  The switch was charred and you could see the contacts sparking when it switched on and off.  I replaced the switch and now only 2 weeks later the new switch is also burnt up.

 

My question is, what is most likely to be causing this?  Am I most likely looking at a bad heating element, or a bad contactor?

 

Any thoughts or insight would be appreciated.

Thanks,

Mark

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When you say that the new switch has "burnt up", do you mean that it is no longer functioning, or just that it has some carbon buildup and is sparking?

 

Mechanical pressurestats will often spark when they open, even when brand new. This sparking will  produce lots of carbon buildup on the switch terminals and surrounding area. That's not such a big deal, so long as it continues to function. I'd expect you to get several years out of a Sirai p-stat.

 

Nothing that I can think of that'll shorten the life of those p-stats that much. I'm assuming you wired the new one in correctly? Might also check for a steam leak, as that'll cause it to cycle more often. That might reduce the life of the component to a year or two though, not two weeks.

Yeah I'm completely baffled... I've checked everything... the old one literally crumbled to pieces, and this new one after two weeks is already charred and sticking.  It's almost like its almost like it's getting too much voltage or amps and just cooking right up.  That has led me to believe I've got more of an electrical malfunction ie: contacor, or heating element.  Either way it's quite frustrating

 

BTW - it doesn't do it every time, but it's more than a slight contact spark... significant arcing ( and sometimes a little whisp of smoke), but not every time and some wire damage to the wires at the terminals.

Mark, when you say contactor, do you mean that there is a contactor between the pressure switch and the heating element?

 

One easy thing to check for is the resistance on the heating element.  Just make sure that the machine is unplugged and the wires are disconnected from the element.  Depending on what the wattage rating on the element is you need to see a number in the range of 14-20ohms.  You can use Ohm's Law to figure out what the resistance specifically needs to be on your specific element.  If you don't know how to do this just ask.  Brady or I could tell you how to figure it out.

I'm thinking that your tank is full of scale, which leaves less room for water, and your element is short cycling, ie turns on all the time to create the desired steam pressure and as soon as the steam valve is opened it loses enough steam to make the pressure switch engage again.  I'm also thinking that the element itself is losing tolerance and pulling A LOT of current which is what is frying the contacts on the new p-stat.  I'm also thinking that all the wiring between the p-stat and the element is fried and needs to be replaced.  Old wiring that has been overheated like that changes is resistance and gets hot.  You could also have poor wire connections at the p-stat, which will induce arcing of its own.  The easiest way to check for these issues is, with the machine unplugged, wiggle the wires, and if the insulation starts to crack and if the wires are stiff then they are adding a lot of resistance to the current.  Also check for the resistance value of the element.  And it would be a good idea to check the fill probe for build up.  If there is a lot of build up on the probe it might mean you should crack the tank to see how much scale is inside.  If the scale is covering the element then the element will run way hotter and pull a lot more juice, which will cook the contacts on the p-stat.  Let me know what your comfort level is with tackling this stuff and I'll be glad to help.

Mike - 

 

Yes there is a contactor between the element and the p-stat.  Thanks for the great insight, I will check those things out.

Theoretically, having a contactor between the p-stat and the element is to keep the p-stat from seeing the full amperage of the element.  The p-stat should only be controlling one leg needed to run the contactor and when the switch engages it energizes the coil on the contactor.  P-stats should run a good long time in this kind of configuration since they are not required to break 20amps of electricity that the element is pulling.

Thats why I'm thinking the contacor is malfunctioning.... the p-stat is seeing too much amperage and burning up quickly.... I've got one on order.  Something is causing too much amperage between the parts and this is all I can think of.

 

Mike Sabol said:

Theoretically, having a contactor between the p-stat and the element is to keep the p-stat from seeing the full amperage of the element.  The p-stat should only be controlling one leg needed to run the contactor and when the switch engages it energizes the coil on the contactor.  P-stats should run a good long time in this kind of configuration since they are not required to break 20amps of electricity that the element is pulling.

Just remember to check the resistance of the element.  If the element is losing tolerance then it can pull more current.  Which could be the root cause of both failures.

As a quick aside, not knowing your experience, I've always found it helpful to think about fixing machines in terms of "What is the machine doing?" rather than, "What part is broken?"

A broken machine is still doing something, though not what it was intended to do.  And if I go looking for possible parts to replace I can generally find a bunch and they may or may not help me make the machine start doing what it is supposed to do.  But if I figure out what it's doing first then I can think about parts and I can address each one in the chain to get the machine to behave correctly.  I apologize if you already know this.  I just know from experience that throwing parts at a problem can be a really expensive way to not fix it.  So make sure you follow the problem back to the root cause.

Couldn't find a schematic for this machine quickly... is the contactor on this machine acting with the pressurestat (like on some Lineas) or is it part of a hi-limit or power switch circuit like on some Astoria and Rancilio?

 

Also, what is the actual voltage at the receptacle?

 

What size breaker is the machine on? Some people will run 20 amp machines on 40 amp breakers, which allows the machine to draw way more than rated power in a malfunction scenario. Any chance that's happening here?

 

A useful device for figuring stuff like this out is a multimeter with an amp clamp... this lets you read what a heater is actually drawing, real time. Relatively inexpensive too.

I have to second Brady on his questions.  Everything is connected and affects everything else.  Before you order one part after another make sure you know all the variables.  With a little invested diagnosis/exploration time you get a solution that sticks rather than the question of "Now what could it be!?".  I would also recommend looking at your water filtration.  Moderately hard water can fill a boiler with scale in a few years which will make your element behave like this.  Make sure your water isn't the ultimate culprit.
Thanks for the suggestions, I'll be working on it this weekend... for now, we continue to limp along...

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