baxi duotec noise

[hogy]

I have a baxi duotec 28 installed about 16 months. For the last 4 or 5 months it has sometimes had a loud vibration for varying periods. I believe it to be a resonance of the inner cover according to thyristor firing angle. It lasts for about 5 mins sometime after morning start up and then randomly for about 5 seconds ( as fan speed sweeps through). When on its long morning run it can be stopped instantly by turning off at the thermostat.
Has anybody any ideas? I am going to try a bit of rubber foam between the two covers to see if that damps out any resonance.

Hogy

 

[howmuchlonger08]

Get it checked by a Engineer for correct combustion with a Flue Gas Anl.
If wrong they can be noisy.

 

[Agile]

I have a baxi duotec 28 installed about 16 months. For the last 4 or 5 months it has sometimes had a loud vibration for varying periods. I believe it to be a resonance of the inner cover according to thyristor firing angle. It lasts for about 5 mins sometime after morning start up and then randomly for about 5 seconds ( as fan speed sweeps through).

Hogy

You should have had the boiler serviced at the end of the first year and that would have included checking and resetting the combustion characteristics.

I am wondering just what "thyristor" you imagine is firing inside the boiler?

Tony

 

[Baxmax]

Its part of the " Thyroid " valve

 

[hogy]

what do you think controls the fan motor?
As a fan is speed controled by progressively changing conduction angle (using an integrated thyristor) a veriety of harmonics are produced.
I was considering whether I was experiencing a resonance to a harmonic so produced.
I accept the sugestion that it could be a combustion problem ie fire back but I can hear this two stories away!.

Hogy (C Eng)

 

[nogoodatfaultfinding]

I have a baxi duotec 28 installed about 16 months. For the last 4 or 5 months it has sometimes had a loud vibration for varying periods. I believe it to be a resonance of the inner cover according to thyristor firing angle. It lasts for about 5 mins sometime after morning start up and then randomly for about 5 seconds ( as fan speed sweeps through). When on its long morning run it can be stopped instantly by turning off at the thermostat.
Has anybody any ideas? I am going to try a bit of rubber foam between the two covers to see if that damps out any resonance.

Hogy

If installed correctly by a registered bloke then this boiler has a 2 year parts and labour Garantee so phone Baxi out to it mate.
They will only ask for your post code and contact details and if you do it tom before 2pm they will be there next day.

 

[Agile]

what do you think controls the fan motor?

As a fan is speed controled by progressively changing conduction angle (using an integrated thyristor) a veriety of harmonics are produced.

Hogy (C Eng)

Whilst I cannot comment on the fan specifically used on the Duotec, similar variable speed fans on most other boilers are controlled by a commutating signal in a similar manner to the stepper motors used in printers etc. This enables the fan speed to be exactly controlled by a frequency generated by the PCB controller then enabling the power output of the boiler to be correctly set as required.

I am expecting your problem is caused by a wrongly set combustion mixture which is just as well as its only a simple adjustment rather than an expensive fan or PCB.

Tony

 

[hogy]

Thanks for your sensible and intelegent reply. I forgot how popular such a control method has become. I will call back the installer to check combustion but it does sound very like a speed resonance of the inner pannel so I will also try damping the pannel. It is difficult to demonstrate because of the random nature of the problem ie maybe 1 in 3 mornings for about 5 mins and and 2 or 3 times a day for 5 seconds.

hogy

 

[Agile]

There is a very simple test to confirm if its a mixture fault if the flue is accessible.

When its making the noise, go outside to the flue and put your hand to partially cover the air inlet ( outer ) slots. If its a weak mixture issue then that should stop the noise.

It is essential you keep you head and nose well away from the discharge part of the flue and dont breath the gases coming out if doing that.

Tony

 

[johnnyboy5]

Thanks, I have the same issue with a very recently installed Baxi Duo-tec FE 40, I did your test and the LOUD HUM stopped. I will get the installer to adjust the mix and post the results.

 

[johnnyboy5]

wow, thanks, Baxi engineer came out (two days after I rang) not bad, adjusted a few things ? - noise GONE...now can sleep at night Zzzzz

thanks