CH header tank steaming & Kettling

[bringit]

Vented CH system
Ideal Classic boiler (15y old)
CH header tank in loft

I have a strange problem where I intermittently have very loud banging (kettling) from the boiler, loud noises from the loft header tank which is steaming with boiling water coming down the overflow into the header tank. The water is so hot that it has melted the actual upvc overflow pipe that goes outside the house (melting a joint which spewed water all over the plasterboard ceiling!)

From some research, I have -

1. changed the overheat thermostat in the ideal boiler (step 56 in manual below).
2. Drained system and put fernox cleaner in (we already have a manga clean fitted)

These two steps have not fixed the issue. There are some steps in 57 that replace the thermostat control and sensor lead. Should I be doing this next or has anyone out there got some good advice as to what this could be. I have googled a lot!

Thanks in advance.

http://library.plumbase.co.uk/flipbooks/RE/idcl270ff_22371_t/mobile/index.html#p=23

 

[Terrywookfit]

Try it ...You may get there eventually !!

Or phone a RGI who has a clue.

 

[John D v2.0]

Strange problem? I'd call it a very dangerous problem! People have been killed by boiling header tanks splitting above them.
Get it fixed ASAP!
It must be more than one problem, blockage and faulty overheat protection, both need to be resolved

 

[bringit]

Strange problem? I'd call it a very dangerous problem! People have been killed by boiling header tanks splitting above them.
Get it fixed ASAP!
It must be more than one problem, blockage and faulty overheat protection, both need to be resolved

Thanks for the concern - had thought there may be an expert on here that would have seen the fault before and could offer advice rather than fear, before I go down the expensive route. There will be no deaths here, water is not above any bedroom.

Anyone with some advice as it would be appreciated ? (not fear!)

 

[Mopasgas]

I am an expert in everything except faulting finding making money ,life and the ,universe etc .....Get accurate thermometer/s /sensor on vent pipe to expansion tank.. after cold fire up ,over what time does it kettle ? , many a plastic tank has melted with Hot water ...once you found give the answer ,no guessing I and others try advise you whats wrong.kettling is a clue but doesnt sound right ..John d says its a strange problem .