Airlock in gravity hot water system

[iep]

Are gravity hot water systems (as per the first diagrma in the link below) more prone to airlocks?

http://www.diyhowto.co.uk/projects/open-vented-heating.htm

After years of working fine, a friends gravity hot water system has become airlocked twice in a month.

The first time this happened, the plumber released air from the system by removing a pipe from the cylinder. The second time, the plumber simply turned up the thermostat on the boiler. I guess this will increase the convection rate and so flow through the pipes ot the cylinder.

Is there any likely issue that might cause this to start happening?

Cheers,

iep

 

[kevplumb]

check the header tank has water in it

 

[iep]

Good call. I'll pass that advice along. I'd like to have thought though that the two plumbers who have already inspected the system would already have checked that.

Mind you, the second one admitted that he didn't understand how the system worked because he'd only been trained to work on combi boilers!

Terrifying.

iep

 

[Nige F]

two plumbers
Mind you, the second one admitted that he didn't understand how the system worked because he'd only been trained to work on combi boilers!

Terrifying.

iep

Don`t call them Plumbers - they are probably Gas fitters . All suited+booted and carrying Gas Safe cards

 

[iep]

I gather they work for a well known national supplier.

iep

 

[OLLIE20]

I gather they work for a well known national supplier.

iep

Who might that be then????????????

Gravity systems are more prone to air locks than fully pumped hw circs, especially if it has long horizontal pipe runs

Also as systems age and breakdown, chemical reactions start to take place and hydrogen gets produced in the system which acts the same as air, you can get rid but it can soon reapear

Ideally systems will need 2 be configured correctly, clean and inhibited, or you could just inhibit it, this may diperse the hydrogen for a while

before adding any chemicals you need to be sure its not a primatic cylinder, if it is (easiest way to tell 1 header tank for ch and hw) dont