Boiler firing when heating off

[Astral_image]

Hi all,

I installed a Nest Thermostat E at the weekend using OpenTherm. Boiler is a combi (Baxi 228). It seems to be working okay, but I've noticed that every hour or so the boiler is firing up, even when the heating is off. It seems to be raising the central heating / hot water temps. The boiler itself obviously doesn't have a preheat function, as this didn't happen with the old on/off thermostat. 

Any ideas what could be causing this?

Thanks

 

[DragosC]

Hi there @Astral_image,

Thanks for reaching out and thanks for the picture. Could you tell us please what are your Home/Away assist settings? Could you send me some pictures from there? 

[Astral_image]

Hi, home/away assist is turned off.

It appears that the boiler is heating domestic hot water to 60c, even though the max is set to 50c on the Nest and the boiler's dial.

Thought it might be Bacteria Prevention but that setting doesn't appear on the Nest.

Spoken to Nest and Baxi, and neither seem to know what's going on.

[DragosC]

Understood. The hot water temperature needs to be in between the 65-75 temperature for the correct flow. As for the OpenTherm, it's a modulary system which keeps a constant fire up if it's wired correctly to the Heat Link via the OT1 and OT2 terminals. Please send us a picture of the wiring of the Heat Link. 

[Astral_image]

The central heating temp is set to 65, domestic hot water to 50. The modulation for the central heating is working as expected, it's just that the boiler occasionally fires up to heat the domestic hot water to 60c. I can't work out why, as it never did this before using OpenTherm...

[DragosC]

Got it. Thanks. Could you send us please a screenshot from the Nest app > Settings > Home/Away assist > When Home & When Away and a screenshot from What decides if you're home? 

[Astral_image]

Home/away assist is turned off, and I've played with the settings to see if it made any difference.

I think it's a bug - I've been in touch with Nest and Baxi and neither seem to know what's going on.

[DragosC]

Understood. Thanks. It's possible, it may be sorted out with the next app update.