"Howling" boiler when it starts up

[chssvl]

I have a Glow Worm Flexicom 24CX boiler, which came with the flat (new-build flat, although remained unoccupied or two years, hence why the warranty on the boiler had expired when we moved in). Pretty much since day 1 the boiler makes a "howling" sound whenever it fires up, i.e. when ignition starts rather than the water pump. Sometimes it is a very loud howl, sometimes it's faint and sometimes there is no howl at all. Sometimes there is even a double-howl. I have tried to capture the noise in this video (sound on). Again, just to be clear, it is when the "flame ignites" so to speak and it happens both when using hot water (system without cylinder) or the central heating. It is only when it starts and does not continue afterwards - of course, if the central heating turns off the flame and then ignites it again, then there is usually a howl.

Everyone in this building has the same boiler and I have heard similar howling coming from other flats so I'm assuming it's something to do with the boiler itself. A guy came to service the boiler one day but, annoyingly, when he came there was no howling so he just said that it was what it was and left it at that.

Any thoughts on what it could be and whether it is repairable?

 

[cross thread]

Did he check the emissions readings ? High and low are critical

 

[chssvl]

I'm assuming he did. I'm looking at the report and it says:

CO/CO2 ratio: 0.0007
CO2 reading: 8.8
CO reading: 34

Not sure if that says anything. Have to say that it was pretty quick...

 

[Harry Bloomfield]

Not sure if that says anything. Have to say that it was pretty quick...

It's not so much a 'service', as an emissions and general safety check. A service takes much longer.

 

[cross thread]

High and low are two separate readings that should be taken when the boiler is locked in a fixed mode.

 

[chssvl]

Ah, OK. So seems that I was fooled into a safety check for the price of a service....sigh....OK. Should probably book a proper service then

 

[ianmcd]

Get Vaillant (Glow worm) same company out to service it properly and make sure you mention the noise to the engineer, then if it does it again after they have serviced it they will come back FOC

 

[DP]

I have a Glow Worm Flexicom 24CX boiler, which came with the flat (new-build flat, although remained unoccupied or two years, hence why the warranty on the boiler had expired when we moved in). Pretty much since day 1 the boiler makes a "howling" sound whenever it fires up, i.e. when ignition starts rather than the water pump. Sometimes it is a very loud howl, sometimes it's faint and sometimes there is no howl at all. Sometimes there is even a double-howl. I have tried to capture the noise in this video (sound on). Again, just to be clear, it is when the "flame ignites" so to speak and it happens both when using hot water (system without cylinder) or the central heating. It is only when it starts and does not continue afterwards - of course, if the central heating turns off the flame and then ignites it again, then there is usually a howl.

Everyone in this building has the same boiler and I have heard similar howling coming from other flats so I'm assuming it's something to do with the boiler itself. A guy came to service the boiler one day but, annoyingly, when he came there was no howling so he just said that it was what it was and left it at that.

Any thoughts on what it could be and whether it is repairable?

A proper service would highlight the issue.
You should have two sets of figures. One high and one low burn.

Howling noise would put the CO reading through the roof

 

[old duffer]

my continuos water heater does that when its operating full bore at startup. It's an acoustic effect when exhaust gases rise rapidly and fill the exhaust. Tape a 22mm pipe and blow down it as if you were playing a trumpet. Same effect.

 

[DP]

my continuos water heater does that when its operating full bore at startup. It's an acoustic effect when exhaust gases rise rapidly and fill the exhaust. Tape a 22mm pipe and blow down it as if you were playing a trumpet. Same effect.

This one most likely different.

There is a speed controlled fan that sucks in gas and air which is fed to the burner where it ignites. Fumes and heat blows downwards into a chamber that is wide at the top and wedge shaped to narrow gap at the base. Blockage or restriction at the base will creat buildup of exhaust fumes resulting in flame lift that sound like a fog horn. There are other causes that create same noise

If a flame is starved of oxygen, it lifts off the burner in search of oxygen. This effect is exploited by oxypilot assembly in gas fires

 

[chssvl]

This one most likely different.

There is a speed controlled fan that sucks in gas and air which is fed to the burner where it ignites. Fumes and heat blows downwards into a chamber that is wide at the top and wedge shaped to narrow gap at the base. Blockage or restriction at the base will creat buildup of exhaust fumes resulting in flame lift that sound like a fog horn. There are other causes that create same noise

If a flame is starved of oxygen, it lifts off the burner in search of oxygen. This effect is exploited by oxypilot assembly in gas fires

Ah, this is really fascinating. A random thought but, as the flat remained unoccupied for two years after it was built with the boiler not getting any use during this period, could it be that dust or dirt accumulated creating a blockage in the way that you describe?

This explanation definitely feels like it makes lots of sense. I will get a Glow Worm engineer to service it anyway, although there don't seem to be any appointments until April!

 

[old duffer]

Fan does not "suck in gas", gas flows into the ignition chamber under pressure from the supply regulator.
My system mixes the gas and air before it goes into the ignition chamber (as opposed to being mixed in the chamber)(also has an inverted burner assembly i.e. top down))
A blockage of exhaust fumes would shut the boiler down. The venturi resistance would close the gas regulator valve and initiate shut down. A rush of exhaust air into a chamber will resonate. This is where the sound comes form. It is only at startup, not during operation.
flame in search of oxygen? this is where the vocabulary is important. Any flame needs oxygen to burn. In this specific situation, the lack of "oxygen" should be substituted for "air", the boiler does not operate analysis to determine ppm of 02 lol.
The "lack of air" would cause the flame to burn inefficiently (yellow flame) and so would "waste" gas as it would be released "unburnt" but it would still ignite in the presence of air...its can't search for oxygen.
The oxypilot works by measuring resistance of the bimetallic probe that sits inside the gas flame. No air means no burn, no burn means no gas..i.e. shut off. Modern boiler use electronic ignition, not oxypilot systems and have done for many years.

 

[old duffer]

Ah, this is really fascinating. A random thought but, as the flat remained unoccupied for two years after it was built with the boiler not getting any use during this period, could it be that dust or dirt accumulated creating a blockage in the way that you describe?

This explanation definitely feels like it makes lots of sense. I will get a Glow Worm engineer to service it anyway, although there don't seem to be any appointments until April!

dirt levels that accumulate to fill the radius of the pipe?

 

[DP]

Fan does not "suck in gas"

On a condensing band A boiler?

Old duffer you need to do some further reading. Pray tell how the oxypilot works.
Where did I say boiler uses oxypilot.

Clearly you explanation while has some merit it is devoid of practical functionality. I challenge you to apply a manometer to output side of a gas valve in a band A boiler and check if it indicated burner pressure at full power

 

[old duffer]

Ah, this is really fascinating. A random thought but, as the flat remained unoccupied for two years after it was built with the boiler not getting any use during this period, could it be that dust or dirt accumulated creating a blockage in the way that you describe?

This explanation definitely feels like it makes lots of sense. I will get a Glow Worm engineer to service it anyway, although there don't seem to be any appointments until April!