glow warm boiler

[kofi2003uk]

hello guys,
my boiler had been kettling for some time and i got an enginner to come in and have a look. he thinks the boiler thermostart is set too high and so the boiler is getting too hot. i mentioned limescale in the system to him because a friend of mine said it could be due to limescale.
he however said no as he had drained the system back in the summer last year when he added a radiator in the kitchen.
anyway he reduced the thermostat and it seems to have stopped the kettling.he also said he suspects the thermostat is faulty.
i have since noticed that one radiator in the lounge/hall has started making funny noises.sounds like someone hitting the rediator very gently with a metal object.this happens after the heating has been on for about forty minutes.
this is intermittent but was not there before.
would appreciate if anyone could give me advice on this please?

 

[fitz1]

possibly stat has lost its calibration. knocking would suggest single flow rad stat on wrong pipe, it only knocks when rad has reached temp and is shutting down.

 

[kofi2003uk]

many thanks for the reply,fitz1.would you agree with my engineer that the boiler thermostat needs replacing.will that solve the radiator knocking?thanks