Problems with subcontractor's invoice

I contractually agreed with the general contractor that the heat pump must be able to cool

This was included with the delivery of the heat pump but was not observed by the electrician.

So the problem is the electrician. Correct procedure: electrician —> general contractor

Were warranty claims even transferred to you? If not, your claim for defect rectification would actually be against the [GÜ] (or then the insolvency assets) and it is unlikely that they care about this in insolvency.

If this concerns things that happened after the insolvency, no warranty claims were transferred to you against the subsidiaries and you arranged the defect rectification with the company now commissioned by you, then they can charge you for this, yes. (At least that is my assessment).

See it this way, it could also have happened that they didn’t want to continue working with you at all. Then you would have had to commission a new company and could probably only file the costs incurred as an insolvency claim (where you might see 2-3% back in a few years).