knocking noise from boiler

[jarvo]

hi,

i have a potterton prima 30 b that has recently started making a banging/knocking noise when it comes on.
This happens for both central heating and heating the water.

I have read a few things and i know it could be a few different causes, not enough water in the system, bubbles etc.

Is there anything i can do to narrow down the cause before i call out a plumber.

 

[chrishutt]

The first thing to check is that there is sufficient water in system. If it's a sealed system with a pressure gauge on the boiler, the pressure should be 1 bar or so. If an open system fed by a tank, is the tank water level above the outlet pipe?

 

[jarvo]

Thanks for the replly,

i will take a look later roday.

 

[jarvo]

finally got around to looking at the system.
(been away on business for most of the week)

The system is an open one, the water level is above the outlet valve and about 3cm below the overflow valve.

However the water is brown and full of sludge.

the noise has developed and there is a continous knocking noise from the boiler whilst it is on.

is it possible that the water needs flusing out??

 

[jarvo]

heres 2 images of the dirty water, ignore the fish net i was using it to scope out the dead spiders floating on the surface.
Took a bit of water out to show the father in law as he used to be a plumber/fitter at a power station.
The tank had about a 4 inch gap where dust/dirt/spiders etc could get in.

Think im going to get the system flushed on wednesday, its a 8 radiator system.