Potential overheating gas boiler

[dinners]

Hi,

I have an old Potterton Kingfisher 2 RS100. I think it may be overheating as I can sometimes hear what I think is kettling in the expansion tank. As it's an old big boiler there's no pump overrun or auto-bypass (as I understand it it is able to dissipate the heat safely itself after the valves close). I'm trying to measure the hot water outflow pipe with a contact thermometer to determine if it's a boiler stat issue, but I was hoping someone could help with how much you might expect the temperature to rise following the valves closing and the boiler shutting off.

Thanks in advance!

 

[Agile]

I do not know how you think you can hear kettling in an expansion tank.

Kettling is a sound made by water inside a metal heat exchanger when it turns to steam inside on the surface of the metal.

Generally those old cast iron heat exchangers are quite forgiving. Although a short pump over run would be far better for the boiler.

That is easy to do with any of several electronics solutions.