Hello,

I have a Unic Twin Phoenix which does not build heat/pressure. I get cold water through the groupheads and controls work fine, except of course for steam/hot water. I took the panels off to have a look at the internals. Upon removal of pressurestat cover, I noticed it had a black film which would indicate a short circuit. My question is, do I simply replace the pressurestat or should I consider what caused the pressurestat to fail as I want to avoid putting in a new pressurestat only for it to fail again. Any help/advice is much appreciated.

Curious. The film appears inside the P-stat, and not localized like on a short. Do I also see it on the insulation of the wires outside the Sirai box?

I think the first thing is too test the element for continuity.

Chert,

The film on the outside of box is dust, black soot is only in the box, it was very fine, here is a photo of it once wiped off... doesn't seem to be any fried lines???

Thanks, I will check for continuity.

Bare with me, I'm a bit of a newbie when it comes to electrical... I checked continuity I think... top row read 36, middle and lower rows read 18. OHM reading top row was .04, .02 middle and bottom rows. Not sure I did this correctly...

I think to get an accurate reading, you need to disconnect the wire from one side of the element first.

Rocky

Heritage1 wrote:Bare with me, I'm a bit of a newbie when it comes to electrical... I checked continuity I think... top row read 36, middle and lower rows read 18. OHM reading top row was .04, .02 middle and bottom rows. Not sure I did this correctly...

Unless you have a pretty expensive high accuracy and resolution meter, reading resistances like 0.02 ohms is not realistic. Take your meter and touch the probes together while reading resistance. It will most likely read 0.02 ohms, unless you are actually using a high precision meter, like say a Fluke 87V: http://www.fluke.com/fluke/uses/comunid ... asurements

There are two reasons you want to disconnect one side of each leg, first you can see in the picture the middle and bottom are connected together on the right, so no matter how you read the middle and bottom, they are connected together. In order to read them both, you could connect your leads to the middle and bottom of the left connection. You are now reading two heating coils in series (which is how they are wired). Personally, I would disconnect the left connections on all three, then read the top "row" and the middle and bottom on the left. This will have you read the top coil and the bottom two coils in series.

All the soot on your pressurestat likely came form the contacts, which are likely shot. Disconnect the entire unit from power, gently move the contacts away from one another and see if they look burnt.

Cool, I've got a 189 and it auto-ranges to the .01 ohm range, but I didn't know about the relative feature.

Thanks for pointing that out.

Ira

number9 wrote:There are two reasons you want to disconnect one side of each leg, first you can see in the picture the middle and bottom are connected together on the right, so no matter how you read the middle and bottom, they are connected together. In order to read them both, you could connect your leads to the middle and bottom of the left connection. You are now reading two heating coils in series (which is how they are wired). Personally, I would disconnect the left connections on all three, then read the top "row" and the middle and bottom on the left. This will have you read the top coil and the bottom two coils in series.

I don't think those two lower elements are connected in series. Note that wire connected to the bottom right in the picture. (if you had no wire there, then yes you'd have to assume that the two were in series.)

These machines are a little oddly wired. See the very last page of this tech manual: http://www.unic-usa.com/uploads/media/s ... c4b923.pdf

The heater on/off switch has a live (aka phase, hot) wire that goes to the pressurestat, which splits at the pressurestat and the two live wires then go to the thermal safety (3 switch) and then to the element. There is also a neutral wire from the heater on/off to the pressurestat that goes to the thermal safety and to the element. The live side of that element goes back to the heater switch - purpose is to support the heater light when the element is powered.

If this machine follows that schematic here's how I'd interpret it:


To check this element, remove all wires, including that brass connector and test each element separately. It will probably check out OK. I agree with number9 that you need to check that the pressurestat contacts are not burned.

I think this machine may be a bit tricky for an electrical newbie to deal with. I'd advise getting some help from someone with good electrical expertise.

homeburrero wrote:I don't think those two lower elements are connected in series. Note that wire connected to the bottom right in the picture. (if you had no wire there, then yes you'd have to assume that the two were in series.)

These machines are a little oddly wired. See the very last page of this tech manual: http://www.unic-usa.com/uploads/media/s ... c4b923.pdf

I did misspeak, I was thinking parallel and wrote series. Ugh. The two bottom elements are in parallel. If you look carefully at the schematic, the two leftmost elements (on the schematic) are in parallel. The bottom wires (if you trace them back) are connected together. So electrically, you have two coils, physically you have three. If you want to check all three physical coils, you will need to start removing wires.

Just with pictures, and what your meter has read, I am still going for replacing the pressure-stat. I have seen a number of those contacts in relays and solenoid coils and with that amount of soot on them, I am straight out going to say your contacts are very worn.