Why is Rad. Feed not as Hot as Flow Temp I've Set?

[Mike K]

Why is the radiator feed approx. 24degC just beyond/out of the Vaillant gas boiler (and also at the first radiator), when I've set the flow temp to 53degC? With boiler firing, the 53deg setting is always flashing on and off on the display - does this mean it never actually gets to 53?
Thanks!

 

[ShaunCorbs]

Sounds like it’s trying to modulate the burner low enough for the flow is the flame symbol constant or going on and off ?

 

[Mike K]

Sounds like it’s trying to modulate the burner low enough for the flow is the flame symbol constant or going on and off ?

Flame symbol is constant; I think this is how it usually displays, most of the time.