BoilerFaultCodesRemeha b20 Fault Code
Also written as B20 — same fault.
The Remeha b20 fault code means: your boiler has paused because an external safety device or switch has told it to stop running for a short period.. It appears on 2 Remeha models in our database.
Technical description: Safety interlock: If the contacts of the external interlock (terminals 10 and 14) have opened during heat demand, the boiler will shut off for 120 seconds
What causes the Remeha b20 fault?
This fault occurs when an external safety device, such as a condensate pump or a secondary thermostat, sends a signal to the boiler to stop for safety reasons. The most common reason is that a pump responsible for removing waste water has failed or become blocked, triggering a switch to prevent a leak. It can also be caused by loose wiring or a temporary break in the electrical circuit that links these external accessories to the boiler.
This fault is more common during freezing winter temperatures, as frozen external pipes can cause condensate pumps to back up and trigger the safety switch.
DIY fix possible
Check if any external safety devices, such as a leak detector or condensate pump alarm, have been triggered.Wait 120 seconds to see if the boiler restarts automatically once the safety circuit closes.Ensure any external controls or emergency stop buttons haven't been accidentally pressed.
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Gas Safe Register →Remeha models that show the b20 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Remeha b20 fault code information on this page is sourced and cross-checked against the official Remeha service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026