Irritating Knocking Sounds!!!!

[Simon Anderson]

Hi I was hoping that someone could give me a bit of advice on what could be causing a problem with my central heating system and what course of action I should take. When my oil fired central heating system is turned on it creates a constant knocking sound which appears to be coming from between the two floors in the house and emanates from the area where the flue goes between the floors (may be a coincidence) the knocking appears to be worst when he boiler is on the ignition cycle and then tails off when it is not. It is like the sound of knocking pipes and is starting to really irritate!! Any ideas would be much appreciated, thanks.

 

[meldrew's_mate]

I take it the flue is metal, and expands when it gets hot?
Could it be rubbing against, or being restrained by, the fabric of the house?

Take a look at BS5440 and Building Regs Doc J for recommended clearances to combustible materials (especially where the flue goes through floors)

Have you investigated central heating pipes expansion noise?

 

[Simon Anderson]

No I haven't investigated central heating pipes expansion noise and too be honest on reflection I think that is a more likely scenario than the flue. The flue has a large stainless steel protection cover around it which does not get warm and thus is unlike to expand when the system is running and to the best of my knowledge this runs right to the roof and the external flue.