NIBE 234 fault code

What it means

Exchange sensors flow/return

The return is hotter than the flow. NIBE's own listed cause: the supply and return lines (or their sensors) are switched around. A classic commissioning error that mimics a reversing/valve fault.

UK models this code applies to

From the NIBE service literature we hold (NIBE S2125 installer manual IHB EN 2442-3 731742 — Alarm list) — not a scraped list.

Now the harder half: proving what caused it

234 names a symptom, not a root cause. In the app, the same code opens a guided investigation: what to measure first, the expected values for your exact model, and an honest verdict — including “nothing in this machine is broken” when that's what the readings say.