Delonghi Perfecta Service Case Study – Triacs and Boiler Issues

SERVICEMAN’S LOG – A Case Study – Delonghi Perfecta Plus ESAM 5450 – A Warning for DIY Thermoblock Fixes

The hard ones are the most satisfying so long as you win in the end and it all doesn’t end in flames like this job almost did. I recently had a customer send me in a Delonghi Perfecta Plus, it came with an extra Thermo-block or boiler in a bag and a A4 letter of explanation and its recent repair history.

The machine had originally failed stuck on “heating up”, so the customer said in the letter. I assume it then timed out to the “General” error alarm. The customer took it to the other guys who fix Delonghi machines in Sydney and was told it was a failed Thermo-block which would cost $500 to repair. So he decided to DIY repair and ordered a replacement Thermo-block.

In his own words here’s what followed;

I ordered a Thermoblock and carefully put it in. Turned on machine and all seemed grand. Went through normal set up with rinsing water then tried to make a shot. All the lights went but no water came through. Dry coffee cake.
Turned off tried again. This time general warning. Then showed heating up but didn’t do anything.
Found your blog, gained confidence and started testing. Amp meter showed both elements good but fuses blown. Why did the fuses blow again??? I thought.
Pulled out solenoids to check but then reached the limit of my smarts.

Ok from reading this the answer should have been apparent. But there were 2 things going on here,
1. Fuses blowing and
2. The shot being dry

Also the customer had pulled things apart. Never helps.

On my first inspection I noticed the EV-1 on backwards. See diagram. From here I made an assumption that this could be the cause of the issues. WRONG! first mistake.
So I corrected the valve orientation and replaced the Thermal fuses. Now I made my second mistake. Normally when I replace a thermal block I leave the element disconnected and fool the thermistor and prime the boiler by running a few cold rinse cycles. This ensures all is functioning in the hydraulics (water lines, pump and valves etc) and ensures the boiler does not run bone dry.
This time I just fired it up and to top things off I decided not to screw the thermal fuses to the block just yet, I intended to do it after testing. After all I was watching and I did not want to bugger my new thermal fuses. Don’t do this!

Initially all seemed well, I made a shot all ok but the second shot was dry as the customer had described. Then I noticed water starting to flow down the overflow tube and into the trip tray. I could hear the boiler starting to boil. Shit then smoke! – seriously things got real hot real fast.

Hydraulics of the Delonghi ESAM 5450

Hydraulics of the Delonghi ESAM 5450

Ok Houston we have a problem. The boiler elements are not switching off.

Either the Thermistor or Triac on the board. Perhaps the over hot boiler is causing steam to force back flow explaining the dry coffee shots. This turned out to be half correct.

I pulled off the thermistor and tested on the bench. 104 k ohms at room temperature and 22 k ohms when heated to 150 Celsius. This appeared normal.

Now I had to remove the control board. Always photograph and label connections. The triac tested faulty using my signal tracer. It showed a diode connection between MT1 and MT2. I removed it from the board and confirmed it had a short between MT1 and MT2.

Label the connections

Label the connections

In order to replace it I grabbed an old Delonghi board and removed the Triac from it. It tested ok with the multi meter. But it wasn’t . It turned out to be open circuit between MT1 and MT2 and the Thermo-block failed to heat. This wasted more time. I checked the records and the Thermo-block from the machine the old board had come from had been good. The machine was acquired from ebay as parts so I guess these Triac’s are a theme on the Delonghi machines.
Note to self -get a Triac tester!

triac removed

Anyway I found another Triac on another old board (surely not 3 in a row) and did the job again. This time the Thermo-block heated and was stable. I made one coffee shot and then the next was dry. What the hell! Again water was flowing out the overflow and into the drip tray. This means either EV1 is faulty or the over pressure valve on the pump is faulty intermittently.

I changed the over pressure valve on the pump and all of a sudden the rinse and good flow and the coffee shots were rolling off and nothing was going down the overflow.

Now the problem is obvious a failed Triac on the board caused the Thermo-block to over heat which caused flow back of hot water which damaged the over pressure valve and blew the fuses.

So a warning. If the fuses (often both go in a thermal event) have blown be sure to check that the elements are switching correctly or you will be again replacing them and potentially damaging a good Thermo-block. Also don’t get sold a new Thermo-block or a new Control Board when a $3.50 Triac is all that is required. Meter the elements first and send your board to us for testing. or just replace the Triacs anyway, they are cheap.

Note also the original Thermo-block the customer sent in the bag tested ok. Bravo for that!

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