It's f***ing freezing - Truma Combi Boiler - C2 PCB Troubleshooting

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The Truma Combi Boiler C6002 in our van no worky at all

Brief diagnosis showed that Fuse F1 on the PCB had blown, the fuse type is a 5mm diameter x 20mm 6.3AT (T is slow blow) glass body fuse. Very easily sourced from Radionics, click and collect the same day, pity the problem manifested in Donegal on a double bank holiday weekend. Ah well, we were on a campsite with EHU because our tent camping friends were crazy enough to tent camp in March in Ireland, so EHU and the rooftop aircon unit switched to hot saved the day.

Back on topic, I got a pack of 10 replacement fuses on my return to Dublin and because there was a similar 1.6AT fuse on the board, I got a pack of 10 of those as well, determined to never be caught out like this again. I replaced the blown fuse and turned on the boiler on followed by a bright flash (gotta love glass bodied fuses) and puff it was gone again.

Time to get serious, I removed the PCB to get a closer look. Replacements don't look cheap, if they can be found. A quick visual inspection identified a bit of charring.



My initial thoughts were that one or both of the resistors were blown and needed replacing or what I identified as the silver thing beside them might have a problem. I bounced this of an electronics guru that I work with on occasion, he identified the silver thing as a heatsink over a MOSFET, most likely acting as a voltage regulator, he noted that these can fail.

Next I replaced the fuse and connected a small 9v battery to the DC Input for the board and probed the MOSFET pins to check their voltage relative to the ground, all 3 pins registered at 9v which to my simple mind confirmed the short circuit.

Have you ordered the heatsink past and new insulation pad also?

Still trying to find the right heatsink, the existing one broke off at the mounting pins and could be reworked if I can't find the right one. The MOSFET has a small integrated heatsink plate, the heatsink sits over the body of the MOSFET wirh metal to metal contact for heat dissipation.

There is no insulation pad on this board.

For the main motor.
The air induction motor sits below the main unit in a "clamshell" ... but it only draws about 1 amp and is switched by another little board beside it.

I'm on the third PCB. The original started registering a false low voltage and preventing the unit from starting up. The replacement developed a fault which immediately shut off the gas valve, no start up again.
Keeping fingers crossed the third one gives a decent lifespan. At €400 a pop you don't want to be replacing many and now replacements are getting hard to find.

Finally got round to taking a look at the motor as suggested



@JJF is on the money with the root cause at the motor. The brushes don't look too bad but it looks like the schottky diode (little barrel shaped component} has blown. I think this may be above my pay grade as regards repair of the motor so I need to source the correct replacement motor.

You’ve got a short in one of the commutator ring circuits in the motor.
If you can get me a pic of the motor I may have a second hand one.
The mosfet blown on the board is usually a pretty solid sign of a motor issue.

I don't envy you getting spares or paying for them, leisureshopirec are selling Truma parts. A 4mmx12mm bolt&nut for £6.30, talk of a rip off. And their would be postage on top.

The PCB is obviously sensitive to the power draw of the motor so if I have to use a different motor, it may be a case of using the existing power supply from the PCB to switch a relay and use a separate 12v feed to power the motor.

Nor much in the way of identifying marks, CF6F on the end cap

The Diode is more likely to prevent back EMF damaging the PCB when the motor shuts down, there'll be quite a bit of inertia in the impellor wheel. There's been a bits of debris come out of it as well, the windings may be OK but it would need to be rebuilt by someone who knows what they're doing more than I do.

There is a guy in tbr UK rebuilding and repairing both the board's and motor's.

@JJF, do you know what the RPM of the Truma motor is.?

Good job we have youse boys. This technical stuff is gobblygook to me

Back in office later, will PM you.