Kettling boiler

[NickH]

Any ideas what could be causing this ?

Its a conventional open vent system, BG 330 boiler with pump overun (working OK) , S plan, 2 x 2 port valves (one for DHW, one for Heating) grundfoss pump and auto bypass fitted, no trv's.

We are doing extensive refurb works on the property (not the heating system) and are "trying" to stop the boiler kettling. Firstly, the system was incorrectly wired and so ran constantly (24 hrs), the boiler was turned down to 1 1/2 and so it just ticked over, never getting up to temp. When I had the wiring fixed (link removed) and turned the boiler up, bingo the kettling started.
Basically the boiler kettles LOUDLY for about 5 minutes whenever the system comes on but then settles down and runs fine, all the rads get hot and the cylinder heats up. If the system switches off, even for say 5 or 10 minutes and then comes back on the kettling will start again for another 5 mins and then settle down. Pump speed doesn't appear to make any differance.

I drained the system a couple of weeks ago and refilled with sentinael X400 which is still in the system.

Any ideas or suggestions would be greatly appreciated.

 

[Cds]

Kettling is caused by localised hot spots which result in bubbles of steam. When these collapse (implode) you get the loud banging noise associated with kettling. The hot spots are caused by either poor flow over the boiler surfaces or deposits of scale.

Check that there is adequate floe when the boiler fires up perhaps a valve is a bit slow to open, try setting the valves to manually open to see if this overcomes the problem. You could also try flushing the system after adding a suitable scale remover.

 

[Blackcatgas]

Kettling is caused by localised hot spots which result in bubbles of steam. When these collapse (implode) you get the loud banging noise associated with kettling. The hot spots are caused by either poor flow over the boiler surfaces or deposits of scale.

Check that there is adequate floe when the boiler fires up perhaps a valve is a bit slow to open, try setting the valves to manually open to see if this overcomes the problem. You could also try flushing the system after adding a suitable scale remover.

Couldnt have put it better myself.