BoilerFaultCodesYour boiler has paused because an external safety device or switch has told it to stop running for a short period.
This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.
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 this 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.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Protect yourself from future repair bills
A boiler cover plan would cover faults like b20 — no call-out fees, no surprises.
Affiliate links — we may earn a commission at no extra cost to you.
Remeha Quinta 30 is discontinued — time for a new one?
Parts for discontinued models can be hard to find and expensive. A new A-rated boiler could save you money on both repairs and energy bills.
Affiliate links — we may earn a commission at no extra cost to you.