Ideal Classic NF260 making "howl" noise

[civilian]

Hi,
I have a 16 year old Ideal Classic NF260 which is working fine except that when running the CH it makes a howling noise a few seconds after it fires up. The howl comes and goes for the next minute or so and dies away, then starts again when the boiler refires It seems worse when the weather is cold, and usually takes about 15 mins from when the CH first comes on until it starts doing the howling. The noise is quite loud inside the house, but even louder outside by the flue outlet. Seems like a pure sine wave - the wavelength is one quarter the length of the flue according to my O-level physics (about 40cm), so could it be some kind of standing wave? So far BG have changed the fan and cleaned the heat exchanger, but I really think they have no idea, and given the boiler age I don't want to throw a lot more money at it, if a new boiler is the only answer.
All ideas welcome. I can email a recording of the noise if it would help anyone with a diagnosis.
Thanks
Tim

 

[SimonJohns]

I would say that you may have a flow rate issue through the heat exchanger. So maybe a clean of the water ways in the he or check pump speed. If its on 1 turn it up to 2

 

[civilian]

Thanks for the quick reply. I checked the pump and it was on number 2 so I increased it to number 3. So far the result is impressive - I noticed one slight hoot this morning, but nothing like as bad as it was before. Fingers crossed that the problem stays away. Is there any implication for running the pump on 3 instead of 2? There are 16 radiators in the house (12 single and 4 double). Thanks Again.

 

[SimonJohns]

I wouldn't worry too much. But I would start saving for a new boiler

 

[mitchellplumber]

Give your system a clean out.

 

[civilian]

There is a label on the boiler (dated 1995) saying the system has Sentinel x100 in it, and I know it has never been drained/cleaned since. When you say "clean" the system, are you suggesting I should go for a powerflush or just a drain and refill with fresh water and additive?

 

[CES]

If you are having problems with your radiators not heating then maybe you should consider a power flush, if not then get a bottle of either X400 or Fernox F3 and put it into your small header tank in the loft (the one with the brown water in it just to clarify). Run your CH system as normal for up to a week and drain down.This is a system cleanser that breaks down any accumulated sludge. Refill with fresh water and add either a bottle of Sentinel X100 or Fernox F5 into the same header tank. This is inhibitor which removes dissolved oxygen from the water in order to slow down or "inhibit" the corrosion process.
I would also recommend a magnetic filter, Magnaclean or Fernox TF1 be fitted into your heating system, this will hold any magnetic particles in your system water and help protect your boiler.