BoilerFaultCodesWhat the manual says
Manufacturer manualPower on, CH demand, HW demand, Burner on flashing (Fan/APS fault)
From this model's manual
Verified against the Worcester Bosch 24 28cdi Ii Rsf installation & service manual.
What causes this fault?
This fault occurs when the boiler attempts to start up but cannot establish a stable flame to stay running. The most common reasons include a blockage in the gas supply, worn-out spark electrodes that can no longer ignite the fuel, or a control board that isn't sending the correct signals to the gas valve.
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.
Find a Gas Safe engineer
Search the official register →
Boiler cover options
Avoid the next call-out bill
A cover plan would handle faults like FAIL POINT J: no call-out fees, no surprise bills.
Approved partner
Get a quote →
Domestic Appliance Guard
Unlimited call-outs, 24/7 helpline, no price-hike promise
Affiliate links. We may earn a commission at no extra cost to you.