Code C5 with Vitodens 300-W

[PierreH57]

First of all, I'm sorry but I've to write this in english as my german isn't good enough.

I recently acquired a house in France equipped with a Vitodens 300-W but the main thermostat of the house was gone. I replaced it with a wireless tado thermostat (a professional electrician installed it on the 300-W) and have installed tado thermostatic heads on every single radiator that I have.

But now everytime I raise the heating, the 300-W heats until 40°C ish then I have the error code C5. I did like I've seen on this forum and changed the programming code 2 - 30:2 to 30:0 and then it works. The issue is that the programming goes back to 30:2 after a couple of hours ( and it changes back every day), so I've to go and change it pretty much each time I need some heat. Does anyone know why it goes back to 30:2 ? Is there a way to make it stay at 30:0 ?

Could it be because there is some daily programming into the 300-W and the programming code changes for each time slot ?

Thanks in advance,

Pierre

[HerrP]

Hi @PierreH57 !

C5 indicates a KM BUS communication error regarding the speed controlled heating pump. 30:0 is only for service. After a while the automatic system detection switches back to 30:2. Disabling automatic detection may work by E5:0.

Anyway, try to pull off and put on again the KM BUS connector (on the controller board) of the pump a few times. Perhaps there is only some oxidation of the contacts and you may fix the issue by clearing that oxidation.

greetings!

Phil

ps. if this does'n help, perhaps it works to keep the connector removed and switch to E5:0 and 30:0

pps. you may receive the complete documentation of your system when entering the S/N (7.....) of your heater

on https://www.viessmann.com/etapp/parts/en/0500/

[PierreH57]

Hello, 

Thanks for your answer. I checked every connection but there wasn't any oxidation anywhere. I also checked the programming and E5 was already set at 0.

I didn't try to keep the connector removed because I had a professional come at my house today for the annual checkup of the machine so I thought I would ask him. He told me that the TADO wireless V3 thermostat isn't compatible with my machine (which has an exterior temp sensor and heat regulation) and that is the reason of the error. Whenever the TADO thermostat requires heat, the machine does nothing, but when I turn the wheel (to set confort temperature) the boiler starts right away. 

So as for now I'm not quite sure what to do, as I already invested quite some money in my TADO setup.