BoilerFaultCodesWhat the manual says
Manufacturer manualWater circulation fault (Differential between flow and return thermistors too great)
What causes this fault?
This fault occurs when the boiler detects that water is heating up too quickly because it isn't being pushed around your radiators fast enough. The most common reasons are a pump that has seized or failed, a blockage caused by sludge in the pipework, or air trapped within the system preventing flow.
This issue is most common during the autumn when heating systems are turned back on after being idle all summer, which can cause internal pump parts to stick.
Engineer required
This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Avoid the next call-out bill
A cover plan would handle faults like F23: no call-out fees, no surprise bills.
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Related fault codes
All 70 fault codes on the Ultracom 35 Store
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