Nest H73 error code

[Darren2240]

Viessmann Vitodens 100-W has been working fine with Nest smart thermostat for several weeks. Using opentherm technology. All of a sudden I’m getting a H73 error, suggesting unable to detect opentherm connection. Seems to have coincided with WiFi outage.

Any ideas on what to do?

[Mike21]

Did you get this problem resolved? I'm asking because I have the same boiler with Hive Active Heating On/Off control & I'm contemplating changing to opentherm.

Where did you get that error code? I've just been looking on the Viessman error code lookup & it seems that their error codes are in hexadecimal, with characters in the range from 0-9 A-F, so H73 doesn't seem to be a valid error code.

Have you reset the Nest and reconnected to WIFI? Bit should operate in stand-alone mode without WIFI

[Mike21]

ah, sorry misunderstood, this is a Nest error code! Sound like the Nest and boiler aren't talking over OT, or perhaps the Nest has become confused. The help talks about loss of boiler power as a possible cause, so still think a Nest reset is probably the answer.

Surprised you haven't had a response from Nest Technical support on this.... beginning to reconsider Nest as a possible choice if there isn't any good tech support...

[Dimsum]

Ive got this error code and can’t get rid of it straight after set up. 

[AlexD]

Thanks for reaching out @Darren2240 and @Dimsum . I would be happy to try and assist both of you.

The H73 message indicates a wireless connection between the Head Unit (display) and Heat Link is established, but OpenTherm is not detected. Let us gather some details on this:

1. What type of Nest thermostat do you have? The 3rd Generation or the E version. 

2. Did the issue occur during installation?

3. Was it installed by a Nest Pro or by a professional installer?

4. Does the boiler have the OpenTherm logo shown here or was it installed using an adapter/E-bus?

[DragosC]

Since I haven't heard from you in a while, I'll have to close this thread. Should anything else come up, please open another thread and we'll take it from there. Have a good one and stay safe!

[george_t]

Hi @Dimsum, @Darren2240. Did you manage to check the message from my colleague?