BoilerFaultCodesYour boiler has detected that water is not circulating correctly through the system, causing it to shut down for safety.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Flow check failed
What causes this fault?
This fault occurs when the boiler's internal sensors detect that heated water isn't moving away from the heat exchanger quickly enough. The most common reasons are a seized or failing circulation pump, a build-up of sludge blocking the pipes, or simply air trapped within the system preventing flow.
This issue is more frequent in autumn when heating systems are first turned back on after being idle all summer, which can cause internal pump components to stick.
DIY fix possible
Check that the central heating pressure gauge is between 1 and 1.5 barEnsure all radiator valves are fully openCheck that the boiler isolation valves underneath the unit are switched to the open positionReset the boiler using the 'R' or Reset button
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 104 — no call-out fees, no surprises.
Affiliate links — we may earn a commission at no extra cost to you.
Could it be time for a new boiler?
If repair costs are adding up, a new energy-efficient boiler could be the smarter long-term choice.
Affiliate links — we may earn a commission at no extra cost to you.