BoilerFaultCodesYour boiler is receiving a specific signal from an external control or accessory that it doesn't currently know how to handle.
This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.
Technical description: Signal "External demand" on circulation pumps: See table in manual (Address 34:1)
What causes this fault?
This fault happens because the boiler is receiving a request for heat from an external pump or accessory, but its internal settings are not configured to recognize that specific signal. It is essentially a communication mismatch where the boiler’s software is told to expect one type of instruction but receives another. This usually occurs following a new installation or a control system upgrade where the technician forgot to update the digital 'address' in the boiler's menu.
DIY fix possible
Locate the reset button on the front control panel.Press and hold the reset button for 2 to 3 seconds.Wait for the boiler to restart; if the code returns, contact a professional to check the system configuration.
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 34:1 — no call-out fees, no surprises.
Affiliate links — we may earn a commission at no extra cost to you.