BoilerFaultCodesTechnical description
Boiler is in waiting period of modulation f block function due to water shortage
What causes this fault?
This fault occurs when the boiler's sensors detect that the temperature inside the heat exchanger is rising too quickly, which usually means water isn't flowing through the system fast enough to carry the heat away. The most common reasons for this are a failing internal pump, a build-up of sludge or debris blocking the pipes, or air trapped within the unit. To prevent overheating, the boiler temporarily pauses its operation to allow the temperature to drop back down to a safe level.
This issue is frequently noticed during the first cold spell of autumn when the heating is turned back on after being idle all summer, which can cause internal pump parts to seize.
DIY fix possible
Check that the boiler pressure is between 1.0 and 1.5 bar on the displayEnsure all radiator valves (TRVs) are fully open to allow water flowCheck that the blue isolation valves underneath the boiler are in the 'open' position