Calling a person who has a different opinion to your opinion does not make your opinion any more valid.
I had already realised that the boiler was responding to flow before you confirmed that was the cause,
Counting a few more pulses would further delay the start of heating the hot water but the extra delay before firing would be short in comparison to the time it takes for heat to get through the heat exchanger from flame to water.
Muggles suggested maybe fitting a mini expansion vessel
In hydraulic terms a dead leg with trapped air is the same as an expansion vessel with trapped gas ( nitrogen or air ) except that the expansion vessel has a membrane separating water from gas.
If you truly were the font of all knowledge you would know where the mini expansion vessel goes in relation to the sensor it's not rocket science.
And before you run to the mods please note I never called you names I said you was acting like one - as usual