Can I fix Baxi E.01.12 myself?

No. It needs a Gas Safe registered engineer to diagnose. Tell them the exact code and your boiler's model name.

E.01.12Baxi

Baxi E.01.12: return temperature higher than flow temperature

Checked against Baxi's own documentation: Baxi: boiler error codes. Last reviewed October 2026. How we check

Engineer only

Baxi describes E.01.12 on Baxi Combi 2 and System 2 (200, 400, 600, 800, Assure 500) boilers as: return temperature higher than flow temperature.

There is nothing you can safely do yourself with this one. Leave the boiler off and book an engineer.

Write down the code exactly as the display shows it: E.01.12.
Find your boiler's model name. It is usually on the front panel or in the user manual. The table below shows why it matters: Baxi codes can mean different things on different models.
Note when it started and what the boiler was doing (heating, hot water, or starting up).
If the boiler is still under warranty, check your warranty paperwork before you book anyone.

Find a Gas Safe engineer near you Opens the official Gas Safe Register search.

Applies to Baxi Combi 2 and System 2 (200, 400, 600, 800, Assure 500). Codes can differ between models, so check your manual.

Model	Meaning
Baxi Combi 2 and System 2 (200, 400, 600, 800, Assure 500)	Return temperature higher than flow temperature

Model

Meaning

Baxi Combi 2 and System 2 (200, 400, 600, 800, Assure 500)

Return temperature higher than flow temperature