Boiler kettles only with high setting

[jockademus]

This may have been asked but it is baffling me.

My boiler - very old baxi bermuda back boiler which as boiler settings 1-5 (5 max). The boiler is for the CH and HW. If I set the temp to 4 or 5 and the room thermostat is set on 25, there is very little kettling from the boiler once the room temp has been reached. But if I set the room temp to say 21 or 22, the boiler kettles extremly loud (some banging noises from the pipes as well) when the room temp is reached. But if I set the boiler temp to 2 and keep the room temp at 22, the boiler does not kettle (the only problem with this it takes longer for the rads to heat up).

Is this a case that the boiler (pump) cannot pump the water around quick enough and therefore the boiler overheats the water or is it something else.

Please please help.

 

[ChrisR]

As you probably know, the boiler isn't aware what the room temperature is or what the room stat is set to.

The boiler will kettle more when it gets hotter. It probably needs flushing/descaling, but you could try some "Boiler Silencer" liquid additive.
Could also be a worn out pump.

 

[jockademus]

They may not be connected but it sometimes feels like one knows what the other is doing!

Maybe you can answer this - if the temp setting is low on the boiler, will it take longer to heat the CH?

 

[ChrisR]

Maybe you can answer this - if the temp setting is low on the boiler, will it take longer to heat the CH?

Yes

 

[Agile]

It sounds as if your problem is occuring when the boiler is only heating the hot water, presumably by gravity.

I would say it sounds as if something is amiss. Perhaps the thermostat is out of calibration or the sensor is not thermally well connected. It could be a design fault or a pipe blockage. Or the heat input is set too high ( CORGI job ).

The simple solution is to turn the thermostat down to the point where it does not cause any problem.

The best solution is to get it serviced and the settings checked.

Tony Glazier