BoilerFaultCodesYour boiler is receiving a constant request for heat from an external control or thermostat, causing all the pumps to run continuously.
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: All pumps are controlled
What causes this fault?
This fault happens because the boiler is receiving a permanent electrical signal telling it to keep heating, even when your heating is turned off. It is usually caused by a physical fault in an external part, such as a stuck motorized valve or a faulty room thermostat that is failing to stop the demand signal. Because the boiler thinks it is still being asked for heat, it keeps the internal pumps running constantly to circulate water.
DIY fix possible
Check all room thermostats are not set excessively highCheck if the programmers or timers are stuck on an 'Always On' settingTurn the boiler power off and back on at the fused spur to see if the signal resets
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 34:0 — no call-out fees, no surprises.
Affiliate links — we may earn a commission at no extra cost to you.