Vitodens 050 W A9 error

[Nicolas_]

Hi,
I have a Vitodens 050 W (24kW) used in an apartment floor heating system. Lately I keep getting the A9 error. I've reset the boiler and I've changed the batteries in the wired wall thermostat (Honeywell CM707) but the error randomly appear.

There is also a mechanical thermostat mounted on the floor distribution heating system, wired connected in boiler.

The system settings are as follows: 45*C set on primary heating circuit in boiler control panel, 24*C set on the wall wired thermostat, 40*C set on mechanical thermostat mounted on the floor distribution heating system.

As far as I've read, A9 error in Vitodens 050 W could be related to the thermostat connections but the wires are fine, no changes on this side.

Would you please advise, is there anything else that I can check or change?

Also, the optimal functional regime will be using the higher temperature setpoint set on the boiler primary heating circuit or on the mechanical thermostat mounted on the floor heating distribution system?

Thank you,  

    

[Fiedel]

Hi Nicolas,

please send us the serial number of your Vitodens.

With best regards

Fiedel

[Nicolas_]

Hello, 

Sure, attached. Thank you,

[Fiedel · Accepted solution]

Unfortunately the Viessmann database does´nt know this number.

But if we talk about this heater, A9 says:

A9 Control mode without OpenTherm influence
Communication error, OpenTherm device Check connections and lead; replace OpenTherm if required

Serv.Man.

I would think you should doublecheck the connections of the Honeywell or replace the device.

May be the relay in it is worn.

[Nicolas_]

Great! Good to know, thanks.

[Nicolas_]

I have a question on this subject.

The mechanical thermostat mounted on the floor distribution heating system (not the wall ambient thermostat) should be set at a value higher than the value set in the Vitodens primary heating circuit or lower?

e.g. Vitodens heating set to 45*C, mechanical thermostat mounted on the floor distribution heating system 40*C OR  Vitodens heating set to 40*C, mechanical thermostat mounted on the floor distribution heating system 45*C ? Thanks,

[Fiedel]

Vitodens heating set to 40*C, mechanical thermostat mounted on the floor distribution heating system 45*C

This is correct: This mechanical thermostat ist a safety- thermostat, that protects your floor heating system

from higher temp´s, that might damage it. If too high temp´s go into the floor, this thermostat opens its

switch, and stops the floor heating pump.