Knocking Radiators

[UnderTheStairs]

Hi.

I live in a rented, split level flat. Radiators x 6 are all 24 years old apart from one which is newer, though I'm unsure how recent. 2 rads on lower level, 4 on upper, each with a TRV. Mostly in the evenings, the rads (mainly the lounge rad) knock loudly for 20 seconds or so starting out fast and slowing to a stop. It happens between every 8-20 minutes all night until we turn the heating off. It happens less so in the day and hardly at all after the heating is turned on for the first time. There's also random, singular, loud clunks which can can also happen just after the fast to slow knocking.

Plumber has been and drained/put cleaning solution into each rad. He also removed the TRV on the small bathroom rad which leaves it full on. Water that came out of drained rads that I saw was quite murky. Boiler has no brand on it and is about 3 years old. Plumber thinks its a pipe expansion/rubbing problem and is coming back to potentially lift floorboards in the lounge to check pipework near joists. All rads heat up well but all are hotter at the top than the bottom. The knocking appears to be coming mainly from the lock shield on the lounge rad but also throughout the rad. Doesn't sound like knocking from under the floor. Does anyone know what this could be or sounds like? I'm sure the plumber knows what he's talking about but I'm just trying to research this and get any other information. Wondering if there's anything I can try myself.

Cheers.

 

[mountainman]

Chances are that it's pipe/radiator expansion noises.
Can be easy or difficult to remedy.

 

[UnderTheStairs]

Yeah, this is what the plumber was saying. Said he might take the lounge floor boards up and not find the problem, though I'd imagine if the knocking is on the lounge rad, the rubbing must be from under those boards?

 

[UnderTheStairs]

As an update, I turned the lounge rad off and let it get cold with the rest of the system left on. The knocking reduced by about 90% but didn't stop completely - just small occasional knocks and from the TRV end of the rad this time. Don't know if that throws any light on things. Any help appreciated.

 

[petercj]

Sounds as if you've narrowed it down - might be worth lifting the boards by the lounge radiator.

If there's another radiator of the of the same size and fitting, try swapping the lounge rad around.

 

[MCPH]

Hello, is this a sealed or open vent system?

 

[UnderTheStairs]

Hi Peter and MCPH,

This evening I've turned the system on and purposely left the lounge rad off again. After a couple of hours of proper warming up, the knocking is now back! From this, I'm guessing that it must be the pipes rubbing the joists under the floor boards? If it is, would replacing the brackets and piping and cutting adequate gaps under there mostly solve the issue? Unfortunately, the lounge rad is really long and the only one of its size in the flat. Otherwise, I'd swap it over myself to check as you suggest.

I'm unsure if this is a sealed or open vent system. How would I determine that?

Cheers.

 

[MCPH]

Hi Peter and MCPH,

This evening I've turned the system on and purposely left the lounge rad off again. After a couple of hours of proper warming up, the knocking is now back! From this, I'm guessing that it must be the pipes rubbing the joists under the floor boards? If it is, would replacing the brackets and piping and cutting adequate gaps under there mostly solve the issue? Unfortunately, the lounge rad is really long and the only one of its size in the flat. Otherwise, I'd swap it over myself to check as you suggest.

I'm unsure if this is a sealed or open vent system. How would I determine that?

Cheers.

Do you have a combi boiler (sealed), or system with hot water cylinder (vented or sealed).

 

[MCPH]

Do you have a combi boiler (sealed) or system boiler with hot water cylinder (vented or sealed).

 

[UnderTheStairs]

Do you have a combi boiler (sealed) or system boiler with hot water cylinder (vented or sealed).

Thanks. It's a combi boiler.