Peugeot 406 low heating output

Oh, I feel your pain! Had a similar thing happen with my old Saab, but the symptoms were slightly different. Was yours throwing any weird engine codes before this, or did the heating just gradually get worse? What about coolant level, is it stable?

Coolant level appears stable, and there were no preceding engine codes. The reduction in heating output was gradual. Could you elaborate on the specific nature of the problem you encountered?

Turns out for me it was just a corroded connector on the valve itself. But honestly, messing with coolant systems can be a pain. If you're not 100% confident, I'd say bite the bullet and get it checked by a workshop. Save yourself the headache.

I appreciate your advice. Following your recommendation, I sought professional assistance, and indeed, the water valve was defective. The repair amounted to 95€.