Vaillant VRT370f losing settings

[GiAl]

I have a Vaillant ecotec plus VMW 346/5-5 with a VRT370f thermostat.

I had set the thermostat to a low temperature before going on holiday, when I returned the heating was on, date and time in the thermostat were wrong.
There had been an interruption in the mains and the thermostat had apparently reset date and time but retained the daily settings.

Is this normal behaviour ? I have contacted different Vaillant technical services and got different answers: “yes it is normal, all Vaillant thermostats reset themselves in case of mains interruption, even the more modern like VRC720”; “no, it is not normal, the internal battery is probably empty”; “I do not know”…

Is there really an internal battery (on top of the four AAs located in the base of the thermostat) ? Isn’t there any indication on the screen when it has to be replaced ?

Should there be no settings battery, any suggestion how to overcome this problem ?

Thank you !

 

[RandomGrinch]

Is there really an internal battery (on top of the four AAs located in the base of the thermostat) ? Isn’t there any indication on the screen when it has to be replaced ?

After scouring some YouTube videos, I've found a video showing the insides of a similar VRT350F.
There appears to be a very tiny PCB mounted backup battery/super capacitor (circled):

So yes, it may have a backup battery/capacitor, but it is tiny and I suspect it is only designed to provide power to retain settings for the briefest of intervals (i.e. when changing batteries).

They are also designed to be non-user serviceable and last the lifetime of the device.

...However, the battery backup question is moot!
How can a battery powered, wireless device lose power due to a mains outage?

Was it connected with the eBus link?

 

[GiAl]

After scouring some YouTube videos, I've found a video showing the insides of a similar VRT350F.
There appears to be a very tiny PCB mounted backup battery/super capacitor (circled):
View attachment 289334
So yes, it may have a backup battery/capacitor, but it is tiny and I suspect it is only designed to provide power to retain settings for the briefest of intervals (i.e. when changing batteries).

They are also designed to be non-user serviceable and last the lifetime of the device.

...However, the battery backup question is moot!
How can a battery powered, wireless device lose power due to a mains outage?

Was it connected with the eBus link?

Thank you RandomGrinch, form the pic it seems a capacitor, which, as you say, would only retain the settings for a very limited time.
Your question "How can a battery powered, wireless device lose power due to a mains outage?" is legitimate (and I should have thought of it earlier !).
I have the feeling that the receiving part of the 370f (the one close to the boiler and connected to the ebus) is where the data is stored, and that part is powered by the mains.
When, for example, I change the temperature setting, it takes a bit for the display to show the new temperature, as if it had to be sent to the receiver and somehow acknowledged.
I just made a test, removed the batteries from the thermostat and reinserted them after a few minutes. The thermostat initially did not show the settings, that were restored after a little while, though, (including correct date and time) I guess received from the receiving part.
So if the mains are interrupted, the receiving part shuts down and loses the settings.
This seems to me a severe limitation of the system.
Has anybody had any problems like mine or found a solution ?
Thank you !

 

[RandomGrinch]

So if the mains are interrupted, the receiving part shuts down and loses the settings.
This seems to me a severe limitation of the system.

It's possibly just a glitch; these are basically computer systems.
If you turn one part off, when the other part is expecting data, there can be errors.
I don't think it's anything to get worked up about; just be glad that boilers don't run on Windows!

...but it does show how good Vaillant technical services are!