My radiator is knocking - why?

[Benjaminpalma]

I have a radiator on the top floor of a three-level house. When the heating comes on, it makes a loud repetitive knocking sound - like a slow diesel engine - which dies down after about five minutes.

Any ideas why this might happen and how I could fix it? I have no previous plumbing experience!

Thanks.

[sleep envy]

there's air in the system which you need to bleed out

[evenflow]

It wants to come in?

[PintOfKittens]

evenflow said:

It wants to come in?

Was just going to post that...

[nocarjames]

big softy, no need for the heating yet go and put another jumper on

if you insist you will need one of those small keys to bleed the radiator, just don't turn it too far or you will have water gushing everywhere

[Benjaminpalma]

Thanks very much, guys - I hadn't realised air in the system could cause such a racket...

Yes, I'd have it off at the moment, but it's the girlfriend's house. Ooo-err, missus!

[Arthur Jackson]

Expanding pipe touching on wood.

[Rickyy]

Possibly a faulty TRV, when the knocking noise starts, try adjusting the TRV to see if it makes a difference, assuming it has on fitted.

Either that or what he ^^^ said!

[Simpo Two]

Arthur Jackson said:

Expanding pipe touching on wood.

Yep.

[RemainAllHoof]

nocarjames said:

if you insist you will need one of those small keys to bleed the radiator, just don't turn it too far or you will have water gushing everywhere

Hot water gushing all over you as you panic-hunt for the tiny screw.