Vaillant ecoTEC plus boiler problem

[Brian Drury]

Item Vaillant ecoTEC plus 418 fully condensing boiler

Problem Extremely loud ~ 1KHz whistle

Fault Conditions Only when boiler fluid is cool ~ 13 Deg C AND outside air temperature is below 10 Deg C

History Boiler is about 2 years old The problem started shortly after installation Vaillant sent a technician very quickly at the first request. Nice helpful chap but he had never seen the ecoTEC before and had no idea what was causing the noise.

The noise is a pure tone i.e. sinusoidal. The volume is hard to believe and is mostly emitted from the balanced flue. I have not dared ask but I am sure that the neighbours are unimpressed. It really is deafening.

The fix Mr technician stayed for a couple of hours and eventually decided he would change some software settings to limit full throttle. This appeared to work and the lower throttle setting was not a problem. I tried power cycling the boiler to make sure it would not 'forget' the new settings and it was ok. Probably uses flash memory.

Current Situation Problem came back this morning with a vengeance (outside temp 7 Deg C). Reducing throttle further is not my preferred option. Mr technician said if the problem comes back he would replace bits one at a time until problem goes. This he said is standard Vaillant procedure and I bear the cost which will be significant.

Research General web searches. Boiler noises seem to be mostly attributed to kettling, fan noise and thermal expansion.

Experiment Exploring the theory that the exhaust tube was resonating I tried making a baffle - long tube with holes along its length which I lowered into the vertically mounted exhaust. This was intended to absorb sound but more importantly change the resonant frequency.

Result No change

Request Any ideas?

Regards Brian

[Andrew Gabriel]

Excellent problem description. Looks like you've had some formal problem resolution training?

I don't have an Ecotec, but I have a Keston. When first installed, that gave a very deep note, sounding like a 32' organ pipe, so not quite the same as your 1kHz. I found that the supposedly preset mixture control was miles out, and after adjusting it (requires a flue gas analyser), the problem went away. I think the sound was generated in the gas/air mixer. On the Keston, the gas valve has a simple on/off solenoid control, and uses the inlet pressure in the gas/air mixer to modulate the gas flow, and that in turn is controlled by the fan speed, which is thus the modulation control. I suspect that when incorrectly adjusted, there was a positive feedback oscilation around the control loop formed by the gas/air mixer pressure and the gas flow control, which hit the resonant frequency of the mixer and associated tubing.

I have since spoken to one or two other Keston users who had the same problem and called Keston out. In those cases, Keston extended the air inlet tube to the gas/air mixer, which will have changed the resonant frequency.

[John Stumbles]

Google "Sale of Goods Act"

[Malcolm]

Had what sounds like the same problem. Only happened first thing in the morning when the outside air temp was low. Installer called in a Vaillant Tech (German) who tweaked some software settings which cured the problem. I remebered what was done at the time and told my installer . Sorry but as this was a couple of years agoand anno domini is progressing a a rapid rate, I can't remember what was done but I told my installer & he may be able to remember if you are interested - it involved accessing engineering codes on the boiler controls.

Malcolm

[Brian Drury]

Thanks for the responses.

After reading the installation and servicing manual a few times I figured that the d0 parameter which is described as 'Adjustable heating part load in KW' is the thing my technician was playing with.

The current value is 16 so I have reduced this to 13 and the boiler continues to heat to the same flow and return temperatures but it is taking a little longer. This should not be a problem. The modulation rate has also changed i.e. most of the burn is now on high where high is now lower.

So now we wait for a cold morning and listen!

Thanks again

Brian

[Ed Sirett]

I've not met this problem on any I've installed. It does sound like a resonance.

It might still be just under guarantee. I'd start by check every plausible component, flue, fan, flue terminal extensions etc. Then check the combustion settings. Then give the burner assembly a thorough clean out.

Finally replace parts in ascending order of cost/unlikelihood Flue, fan, gas valve, main burner.