bang in radiator pipes

[foxy1]

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

 

[migoplumber]

the boiler installation manual, does ask for 28mm connections from the boiler, this means technically you have a sub standard installation.

knocking noise in radiators when turning on off is usually along the lines of a faulty expansion vessel if its closed circuit?

or a form of blockage anywhere in the system, the water is trying to circulate and hitting a brick wall as such

could be the pump itself

firstly check there is enough air in expansion vessel

good luck
shaun

 

[foxy1]

Thanks, I've pumped up the expansion vessel a bit, I will see if it makes a difference. How do you know how much air you need in the vessel whether there's got enough?

Regards,
Foxy

 

[Bernie2]

Could it be a bit of "kettling" is the automatic by pass valve okay?

Check the Flow and Return temps should be between 10C and 20C differential. Have you bled all the air bleed points in the system?

Some boilers have heat exchanger "kettling" flow problems if you use tight elbows close to the heat exchanger.

Just a few random thoughts, don't know if they are any use or not.

 

[migoplumber]

expansion vessel sizing and pressure depends a lot on your system

generally ive found 0.5 bar below operating pressure is normal. there are however standards and charts to adhere to.

good luck
shaun

 

[feltham]

when i done the unvented corse i had a feeling they said the pressure in the vessel should be one and a half times the working pressure at the hot water cylinder
can some one confirm this tho as i could be gettig mixed up with when pressure testing pipework