BoilerFaultCodesYour boiler has timed out because it has been trying to heat your hot water cylinder for too long without reaching the required temperature.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Maximum charging time for a storage without own controller
What causes this fault?
This fault occurs when the boiler detects that it has been running for an unusually long time without successfully heating your hot water cylinder to the set temperature. The most common reasons are a faulty sensor failing to report the correct temperature or a mechanical part, like a valve, getting stuck and preventing hot water from reaching the cylinder.
This issue is often more noticeable in winter when the incoming cold water mains temperature is lower, forcing the boiler to work longer to heat the cylinder.
DIY fix possible
Check that the valves on your hot water cylinder are fully openEnsure your thermostat or programmer is calling for hot water correctlyTry resetting the boiler to see if the fault clears
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 D.75 — 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.