DS5 Low Heating Output Error

Sounds familiar. I had a similar problem with my old Opel. Also heating issues and error codes. Have you checked the engine coolant level? Low coolant can cause those symptoms. It could also be a valve blockage.

Coolant level is fine, I checked that already. Was it also the water valve on your Opel, or something else?

On my Opel, it turned out to be corrosion on the plug of the water valve. The valve itself was okay. Given the symptoms and error code, I'd still consider getting it checked by a workshop to be sure. They can properly diagnose the valve's functionality.

Thanks, I appreciate the insight! I'll check the plug first, but a workshop visit sounds like the next logical step if that doesn't fix it. They quoted me 95€ for the repair, so it hopefully won't break the bank.