Radiator knocking?

[speshfesh]

CH has developed a knocking at one of my downstairs rads.

If I turn to TRV down a little, it stops buts comes back after a while.

I did read somewhere that this can be caused by a TRV being installed on the flow instead of the return (or vice versa), I can't remember but I'm sure my TRVs were capable of being installed on either(?).

System bled and operating fine apart from this.

Any advice welcome, thanks.

 

[buck51]

You need to check the TRVs again,

 

[speshfesh]

Thanks for the reply,

Do you mean in relation to where they can be placed or for general operation?

 

[doitall]

The pressure differential exceeds the manufacturers parameters.

Do you have a by-pass valve.

What speed is the pump on.

 

[speshfesh]

Sorry guys getting a little over my head.


All running off Biasi 24S (96,000 BTU capacity).

Not sure of the BTU of the rad itself but it's a fairly large one (hallway) I guess 1800x600 in size.

Bypass valve?

Sorry if I'm being a bit dull.

 

[doitall]

The By-pass is built in on that model.

How many radiators have you got on.

Take the head of the TRV off and try it.

 

[speshfesh]

I've got the one already mentioned and 8 others (all around 800x600) + a heated towel rail in the bathroom.

Am I over the capacity of the boiler?

I'll try taking the TRV head off. If that cures it, should I be changing the TRV for one more suitable for the rad?

Thanks for your time.

 

[doitall]

Are they all turned on.

No, you are under capacity as far as the pump is concerned.

It could be the valve is worn and the spring is weak, so a new valve may help.

I'm not sure if you can on that boiler but turn the pump down one notch if it's possible.

 

[kevplumb]

fffff oohh sounds like magnetitus habitus slimus to me

severe case of black rad worm

 

[speshfesh]

I think I can vary the pump speed iif I remember rightly so I'll try that.

TRV is quite old now actually and a visible inspection shows it could be worn and a bit 'battered' so I'll change that I think.

Actually they are not all on (TRVs down to zero) as our upstairs get quite warm, not always need these rads on unless it gets really cold to be honest (mid-terrace gives us some benefit).

Thanks for the help, I'll post again if I don't have any luck.

p.s. rad is clean, as is the system, at least it was when I drained it recently to re-do some pipework.

 

[doitall]

Thats is the problem.

The pump pressure is too great, causing the valve needle to bounce, turning all the rads on would solve the problem.

Turning the pump down would help, provided it doesn't effect the boiler operation.

The best cure if you have most of the rads turned off would be to fit an auto by-pass valve in the circuit pipework.

Look up AVDO. it connects between the flow and return pipes. more inf if required.

 

[speshfesh]

You're a star,

Thanks for your time.