bang in radiator pipes

[womble]

Hi,

I have a Keston C40 boiler that emits loud bangs in radiator pipes from time to time. It seems to happen when the boiler is shutting off in CH mode.

I had a Keston engineer in but all he said was that the flux and return pipes were too small (22mm instead of 28mm) and that there was no point looking at anything else before this is fixed. I'm a bit skeptical as the boiler has run satisfactorily for a year with these pipes.

Before I go through the expense of upgrading the pipes (that would only be on 2-3m from the boiler to the first pipe junction anyway, can't do more), I'd rather check if the problem can come from anywhere else, like an air lock.

Any idea? Is there any manual vent in these boilers or do they went automatically?

Regards

 

[Slugbabydotcom]

Let me help you through the fog that you see before you.

1 Flux is what we use when we solder pipes and fittings together
2 a Flow pipe carries hot water to your Rads from your boiler
3 a Return pipe carries water from your rads to your boiler for re-heating
4 You 'need this pipe renewing' means that your system was installed by a numpty who didnt follow the spec and probably never flushed the system properly either.
5 Your problem is probably related to this numpty because the dirt left in your system has perhaps fouled a diverter or pump or other device.
6 What he would say if he wasnt so polite is that if your system was installed to specification he would be happy to find the problem for you provided it was caused by the boiler in some way attributable to its poor or defective manufacture

 

[kevplumb]

three port or zone valve or trv

 

[womble]

Sorry I meant flow, not flux, that was a typo.

With regard to flow and return pipes the manual says that "pipe connections to the boiler must be sized according to the system load, not dictated by the boiler connection sizes", so 22mm may be ok from a design point of view as it's a small house. The guy who installed the boiler did flush the system.

Rather than trashing the whole thing and starting again I'm looking for pointers as to what to check step by step in order to find the actual cause of the problem, e.g. pump, AAVs, etc. Once I know exactly what's gone wrong I will be more prepared to spend money to fix it.

 

[kevplumb]

I'm looking for pointers as to what to check step by step in order to find the actual cause

three port or zone valve or trv

where to start looking