Central Heating pipe vibrating when boiler stops

[Glindsay23]

Hello,

Wonder if anyone can point me in the right direction, one of my central heating pipes (think its the length from the boiler to the first radiator) is vibrating when the boiler switches off. I recently had new radiators fitted and the vibration stopped for about a month but seems to be back now, the pipe vibrated before this. I've tried the basics (bleeding the radiator and making sure the TRV was on the right way), wonder if anyone else has any other ideas? I dont think the pipe is vibrating against a joist as the vibration only seems to occur when the boiler switches off,
Thanks

 

[Vee]

Bypass setting too tight?

 

[SJB060685]

Open vented or sealed system? If sealed where is the expansion vessel situated?

 

[Glindsay23]

Open vented or sealed system? If sealed where is the expansion vessel situated?

It's a sealed system, boiler is a Vokera compact 29a so expansion vessel is located on right hand side in boiler casing, thanks

 

[Chuck]

What's the pump doing while the 'vibration' is happening? Can you describe the 'vibration' in a bit more detail, please? E.g. is it humming like a fridge, knocking a few times a second, slowing down over a period of time, etc. Spare no details. If you are able to make and post an audio recording that would help too.

 

[Glindsay23]

The vibration seems to only happen when the boiler is in the process of switching off with the pump shutting down, it's generally a series of rapid ticking noises which slows down until it stops. It's coming from the ceiling space approximately 4m away from the boiler, I'll try and get an audio recording cheers

 

[Chuck]

it's generally a series of rapid ticking noises which slows down until it stops. It's coming from the ceiling space approximately 4m away from the boiler,

That's the noise of a contracting length of pipe dragging over something. (It's called "slip-stick".)

Usual cure is to wrap the pipe with some hemp lagging at points it needs to slide.

 

[Glindsay23]

Brilliant thanks, I'll get the floorboards lifted then! Thanks for your help