Noisy rads, clicking - not ticking - (bubbles ?) intermittent

[clubsport911]

Background
10 year old system. Has been kept scrupulously clean. Kept very up to date with inhibitor (higher than normal concentration). Several rads have been removed, flushed and then additional inhibitor added to keep concentration high. Aladdin Self-bleed vents fitted upstairs and down (5 up down, 10 in total). Honeywell TRV's - all working normally. No leaks. Pressure good and holding firm at 1.5bar.

Problem
So, when firing up, and indeed sometimes when system hot I get a clicking sound in a few of the rads. The noise is mostly in the downstairs "bypass" rad - which has normal locksheild valves on both sides. This is NOT the "tick tick" of pipes heating, but the easy to recognise sound of micro bubbles perhaps pushing past the valve / TRV.

Sometimes, on some rads, I hear a larger "gurgle" which quickly clears. Note...ALL rads are very hot at the top. No air present when bleeding - even the ones that have been gurgling.. The Aladdins are new and seemingly OK.

I do however know that the boiler (ICOS HE24) self vent valve needs replacing...but cannot imagine how this admits air.

Not all rads do it... the ones that do make the noise, do not do it all of the time.

I'm confused ! - welcome any help.

 

[Brambles]

Is the gurgle when the system starts up first thing in the morning?

 

[clubsport911]

Hi Brambles... it can be at any time - even when system is hot

 

[king of pipes]

What radiator valves are fitted TRV' s ? if so which brand often on some they are not bi directional making them noisey on operation, others your hear the sound of the system water passing through the radiator as the trv closes down . Kop

 

[clubsport911]

What radiator valves are fitted TRV' s ? if so which brand often on some they are not bi directional making them noisey on operation, others your hear the sound of the system water passing through the radiator as the trv closes down . Kop

All rads - except on on upstairs circuit and one downstairs have TRV's. As mentioned in the original post, Honeywell TRV's. They are all on inlet side. The noise [as mentioned] can come from any radiator but I have noticed it from the downstairs bypass rad (no TRV) of late...

 

[Brambles]

If you believe that the issue is triggered by the formation of micro bubbles in the heat exchanger moving into the flow lines, there are a number of technical papers in the public domain (based on domestic heating systems) that discuss the matter. They give you a good understanding as to how micro bubbles form and the speed / volume of their formation.

Generally, the impact of micro bubbles on a system peaks at start up from cold after a previous day of system use.

Firstly, ensure that the system is leak free, that the expansion vessel is properly set up and get the boiler auto air vent repaired.

Minor system changes can make a big (improved) difference to reduce the volume of micro bubbles formed.
Lower boiler exit flow velocity, larger diameter flow pipe immediately after the boiler, vertical pipework immediately after the boiler, rather than horizontal. Obviously a lower boiler flow temperature and increased system pressure also have a positive impact ( albeit I would not take the system pressure above 1.5bar).

From a technical perspective, if the problem persists after optimisation, a good deaerator on the flow line immediately after the boiler (a Spirotec or similar) circa £100 unfitted, will improve the situation.

However, the key is to minimise formation, rather than maximising removal.

You will always get micro bubbles when water is heated - it is called Henry’s Law.

 

[townfanjon]

I assume by self vent valve you mean a AAV , they dont have them pal .
As above I would look at the quality of the Trv / Ls valves .
Why has every rad got Aladdin’s on , did you fit them to help the problem, personally I would ditch all but one of them .

 

[king of pipes]

I assume by valve you mean a AAV , they dont have them pal .
As above I would look at the quality of the Trv / Ls valves .
Why has every rad got Aladdin’s on , did you fit them to help the problem, personally I would ditch all but one of them .

Agree with Town it is possible to pull air in through a alladin style air vent definitely not needed on every rad , these vents are usually fitted on vertical tall radiators where air gets trapped in the upper sections, kop

 

[clubsport911]

I think air may be pulled in via the boiler auto-vent... So will get that fixed, top up the expansion chamber (1.0 bar ?) and see how that goes. I do like the idea of a dearator - good call.

 

[garygvl]

Agree with Town it is possible to pull air in through a alladin style air vent definitely not needed on every rad , these vents are usually fitted on vertical tall radiators where air gets trapped in the upper sections, kop

if its an icos system boiler will have an aav

 

[John.g]

Looking at the spares list, the air vent is installed on top of the heat exchanger so IMO it's vital that it is operating properly otherwise air could possibly be "permanently" trapped in top of the heat exchanger?. If it not leaking water (faulty/leaking) then it's difficult to see how it would draw air with a system pressure > 1.0 bar. It may be stuck closed or full of muck.
As mentioned in another post above can you reduce the flow temperature to see if the noisy operation dies down,

There was one long running post on here re someone who fitted a new boiler to a vented system and just couldn't get rid of the sound of air rushing around the system so he changed it to a unvented system but still had the same problem but if he reduced the flow temperature to < 60/65C the problem disappeared but would re appear again as soon as he increased the temp to 70C, a lot of knowledgeable people on here suggested the problem possibly lies in the boiler Hx, don't know if the problem has been resolved.