boiler knock 5 mins after heating starts up

[microlighting]

We have a 3.5 year old Halstead Eden X Type VBX 30 that works efficiently but it has a loud knocking & vibration period 5 minutes after heating light up. The problem manifests itself for about 5 minutes then all goes relatively silent. It does not happen when hot water only is on. The noise, reminiscent of a low flying light aircraft, is accompanied by vibration in the vicinity of the hot tank, pump & floor in the airing cupboard upstairs. The boiler, immediately below in the garage, also vibrates but less so. We have had it checked by the London Halstead experts who say the heat exchanger has probable contamination & the system requires power flushing but this was done when the boiler was fitted 3.5 years ago. All the rads have been removed & flushed during a major house update session since then. A reluctance to continually power flush is the system age as it is about 28+ years old. I would be prepared to remove the heat exchanger & check it for contamination but although a competent aircraft engineer & D-I-Y'er I am not 'Gas Safe' registered so reluctant to touch it, although I would consider doing so if a registered gas engineer would check it all out & recommission the boiler - but I understand a reluctance for anyone to do so. Has anyone out there any constructive answers to our problem please?
I wish to add that in early March 2010 I added two canisters of Fernox F2 Boiler Noise Silencer but to no avail. The system still carried on as before. We have not run the heating at all since the end of March, just the hot water, for no other reason than we did not require it on. I am now concerned that all the system contaminates are laying there & may cause bigger problems when we do switch the heating on again - what is my next move please?

 

[twgas]

if the noise only occurs on CH the problem is unlikely to be the boiler itself.
What controls/valves etc do you have?

 

[Agile]

I agree!

What effect does changing pump speed have? Normally on '2'.

Have you tried turning off each rad one at a time?

What would you do with a plane that had a shudder for a few minutes after takeoff?

Tony

 

[microlighting]

Thanks to Twogas (Mick) & Agile (Tony) for your quick replies to my query.
Mick, all the controls we have are a Drayton MA1 Mid Position Actuator valve, a Drayton HTS3 Tank Stat. a Grundfos Type 15-50 Selectric Pump & a Lifestyle LP522 system programmer. All, bar one radiator, is fitted with a thermostatic rad valve, there is no room stat etc. or other controls.
Tony, Changing pump speed has little effect what ever on the noise, timing or intensity. No we have not turned off each rad one at a time. I consider this is a local noise to the airing cupboard hot tank, pump & tank stat primarily & the boiler as stated in my original text. As to flying in a plane with vibration shortly after take off I'd try to get it down ASAP.
I have just added some more info to the original text which may make a difference to any further thoughts on this problem

 

[twgas]

Is the rad without the TRV turned off?

 

[microlighting]

Mick,
No that rad has its valves open all the time.
Bob

 

[twgas]

Where in the system did you actually add the fernox, if you put it in a rad and not used heating since it will still be in that rad and doing nothing.
try turning a couple of trv's to max.

 

[microlighting]

Mick,
Yes, the Fernox F2 was added through a radiator. The heating was used for at least 2 weeks afterwards so the noise silencer fluid must have been well mixed in by the time we last used the system.
I am reluctant to use the heating system until it is decided that there is nothing else I should do first i.e. drain the water & sediment off for example, due to the system being dormant for nearly 5 months. I realise that eventually the heating must be started up before any thing can be checked

Bob

 

[jono_h]

Bob,

I have exactly the same problem with my boiler.

Mine makes a noise like it is 'kettling' - the water is being overheated in the boiler and boiling. This can be due to a pump failure, and would result in the boiler tripping out on overheat.

Because the problem only happens briefly on first start up, I have put it down to low water flow when the pump first starts. On CH there's a fair amount of water to get moving, and until the flow is up to speed there's an oppurtunity for the water to be overheated. It doesn't happen on HW as there is significantly less water to get moving.

I haven't found a solution, and I'm happy for someone with more knowledge to point out the flaws in my idea.

Jon

 

[microlighting]

Jon,
"Reassuring" to know we are not alone with this problem. Our boiler has only suffered with this problem since we removed all the rads for a major house work over a year ago. The radiators were all thoroughly washed out & the heating system had my version of a system flush as I connected pipes at each radiator position & ran the water until clear. The radiators were then reinstalled, the system bled & Sentinel inhibitor fluid was introduced. The heating system ran silently before the rads were removed & for a short while after reinstallation then gradually we realised there was this noise gradually creeping into our life. We actually thought it was from low flying light aircraft but unfortunately not.
As the noise has arisen since our house rework & not since the boiler was installed 3.5 years ago we obviously know it should not do this & we are seriously trying to find out why it is knocking. Fortunately it lasts no longer than 5 minutes after heating light up but it concerns my wife greatly so a solution is mandatory!!!! Joking aside the vibration in the pipework, floor & boiler does honestly make me wonder if it will eventually cause a problem if not cured as quickly as possible.
Good luck with your version of this nuisance but the guys on this DIYnot.com are very helpful & have come up with some alternative points I have not heard before so time is arriving when I shall have to start using the spanners & investigating accordingly.

 

[Topscore]

Hi,

Just resurrecting this ancient thread to ask the OP if he ever found a solution to the problem? I am experiencing exactly the same issue with the same boiler, in fact searching for 'boiler vibrating sounds like an aeroplane' brought me here

Cheers