BoilerFaultCodesWhat the manual says
Manufacturer manualT high - The boiler detects a sudden, unexpected increase in the T between the flow sensor and the system return sensor
From this model's manual
Verified against the Alpha/Alpha E Tec Plus Nx installation & service manual.
DIY fix possible
Check that your radiators are turned on and their valves are fully open to allow water to circulate properly.Verify that your central heating system pressure is at the correct level, usually around 1 to 1.5 bar.Try resetting the boiler using the reset button on the control panel.
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Related fault codes
All 37 fault codes on the E-Tec Plus 28NX
Seeing a different code? Every code this model can display, in one place.