Nest 3rd Generation - firebird enviromax condensing outdoor combi installation help

[HaplessAnd]

Evening All

I wonder if anybody on this well informed forum can assist me as I'm left scratching my head as to what is happening with my Nest controls and boiler.
We have had the above Heatpac S boiler installed and wanted to install a 3rd Gen Nest. I have wired it in as below (excuse the L terminal wires these have now been tidied up!).

Problems we have are:

whenever the hot water tap is turned on the CH pump kicks in and rads warm up

I'm a bit baffled as to why this is. Any help would be much appreciated and gratefully received.

 

[stem]

From your post, I assume that it was working OK before you installed the Nest. So.

What was there before the Nest, and how was it wired?
What terminals at the boiler do the wires you show at the nest connect to?
Is there a spare blue wire coiled up next to the earths? if so was it connected to anything before?
Have you changed any wiring at the boiler end?

Based on the diagrams you posted, I would have expected the Heatlink to be wired as below, and without a link between L & 2.