BoilerFaultCodesWhat the manual says
Manufacturer manualLACK OF WATER IN PRIMARY CIRCUIT: PERFORM WATER TOPPING - UP
What causes this fault?
This fault occurs when the water pressure inside your heating system drops below the minimum level required for the boiler to fire up. The most common reasons for this are a leak somewhere in your radiators or pipework, or a failure in the expansion vessel which helps manage pressure changes as the water heats up.
This issue often appears in autumn when the heating is turned on for the first time after summer, as the change in temperature can highlight minor leaks or a loss of pressure in the expansion vessel.
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 21: no call-out fees, no surprise bills.
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