Vaillant ecotec plus 438 droning vibration noises

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Coming up to the second winter with this intermittent droning vibration noise from our Vaillant ecotec plus 438 boiler. Besides this noise it works fine and heats everything up nicely.

It doesn't happen all the time and anytime I call a plumber it never happens! Whenever I have seen this it has always been while the temperature is rising and just before the flame shuts off. But again it doesn't happen every time.

The frequency of this tends to increase as the hot water demand has been largely satisfied. And the noise only lasts a few seconds as per the video.

I finally managed to get a video of it happening. Hopefully now someone can tell me what is going on here? For the longest time it sounded like a motorbike was passing outside the house.

Watch the video and turn up the sound.

 
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That sounds very much like the boiler is struggling to hold a stable flame on its low gas rate. Unfortunetly theres nothing you can personally do, it needs an RGI with flue gas detecting equipment to check over the boilers emmissions at different gas rates to see if there is something untoward, then inspect the burner/seals and gaskets/flue etc etc,
 
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Last April, the droning was cured by adjusting the gas valve at minimum burner.

So almost about a year later after the adjustment was carried out to stop the boiler from droning, it has returned again. It worked fine through the winter. First question, why would the adjustment be needed so quickly again. Second question, the 438 has been derated to work at 28KW. So does the boiler have to be adjusted as a 28KW boiler or still a 38KW boiler?
 
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It is recommended that boilers are serviced every year.

The correct adjustment was made for you but you seem to imagine that was only needed once and that you don't need to have it serviced.

It is a simple adjustment but does need an RGI with a flue gas analyser to set it.

Your boiler was obviously seriously over rated for your property. But setting the max power to 28 kW will mostly have solved those problems.

Tony
 
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I am not even suggesting that I will attempt this myself. The boiler is 7 years old and has been serviced every year since new. For the first 4 years there was no droning noise. Vailliant do the service and had already derated the boiler to 28KW. But the problem was that the service is always done on Maximum burner. And the boiler would never drone during the service visit. I then managed to record a clip and I worked out that the noise was reproducible by putting the P2 programme (minimum burner). I then got a local RGI to come in to service and adjust the gas valve. However even he didn't know if he should refer to the 438 section in the manual or the 428 section in the manual for max and min because according to him a 438 downrated to 28KW should be treated as a 428. Is he right?

Also my question was more around the fact that if the gas valve adjustment has only lasted less than a year, is that a sign of a failing gas valve - or do I just accept that it will need changing every year.

Also is adjusting the gas valve to cure the droning noise considered part of an annual service or is that considered repair. The reason I ask this is, Vaillant ask me each year, if there is any problem with the boiler. Only if I answer NO, will they send out an engineer to do an annual service. If I told them about this droning noise they tell me it's not a regular service and need a repair call out. Hence I had to get a local RGI in last year to do both service and adjustment.
 
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An engineer doing a proper service should check the settings.

But many do not.

If the boiler is obviously not working properly then some RGIs will charge more as a repair. I tend to do that but then I come sooner than a routine service which I do after a week to avoid those who really have a fault.

Again I should tell you that boilers are expected to be serviced every year!

Tony
 
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Point taken Tony about the regular service. And as mentioned my boiler has been serviced annually every year and will continue to do so. I needed to know if a gas valve that needs adjustment twice within a year is a sign of a failing valve or not. And is adjusting the gas valve considered repair or service?

Also if you look at the boiler manual the CO2% figures are all quoted for maximum burner. There are no figures for when on min burner, which is my issue. Even the RGI who came out last year had to phone Vaillant to ask them who just told him to set it to 8% on minimum. For the maximum setting he just set it between the values for both a 428 and a 438 because either way it was within the tolerance levels for both. But he did this only because he didn't know if he should treat a 438 boiler set at 28Kw as still a 438 or a 428.

Those are my questions.
 
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all its done is adjust the heat output I would of thought it should still be treated as a 438, I thought you only had to check the maximum setting on a Vaillant because they say it should work safely across the range if the maximum setting is correct
 
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who just told him to set it to 8% on minimum.
8% CO2 would be fuel lean which is the reason the burner is baffling.

For the maximum setting he just set it between the values for both a 428 and a 438 because either way it was within the tolerance levels for both. But he did this only because he didn't know if he should treat a 438 boiler set at 28Kw as still a 438 or a 428.
.
Both P.1 and P.2 should be set to around 9% CO2 (9.5% with front case fitted).
 
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all its done is adjust the heat output I would of thought it should still be treated as a 438, I thought you only had to check the maximum setting on a Vaillant because they say it should work safely across the range if the maximum setting is correct
:rolleyes:...both offset and throttle require adjustments when carrying out a combustion analysis.
 
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Yeh fair enough steelmasons (y), I was just saying what I got told on a Vaillant installer Corse but I think that was more for commisioning, I didn't want to give any numbers and values as it was my first post and not sure on the rules on giving out advice on gas related problems :D
 
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When Vaillant did the last service they left with the following readings, which was done using the P1 programme. No service prior to the one done in 2016 was ever done using the P2 programme.

0QYy3q6O.jpg



But even with this the droning noise didn't go away.

Last year 2016, the guy who did the service was on speaker phone the entire time to Vaillant, so I heard everything and they told him to adjust the boiler to 8% on the P2 programme.

He adjusted both throttle and offset and brought the figures to 8% on P2 and 8.8% on P1. That stopped the droning noise and the boiler worked fine from Apr last year to Feb 2017. This Feb the droning noise has returned. Now obviously the boiler is due it's next service soon.

CO2% measured over the years 2013 - 8.8%, 2014 - 8.6%, 2015 - 9.1%.

The first time any adjustments to the throttle and offset were made was 2016 and the readings were as mentioned 8.8% - P1 and 8% - P2.


The chart from the actual manual is shown below, which is why I am after a second opinion.

Capture.JPG
 
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How would you know what adjustments were made and where they were made??
Would you know the difference between the offset and throttle?
 
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I have stood next to the engineer every year when they have done the service. And yes I am aware of the difference between throttle (anti clockwise) and offset (clockwise) turns. In fact it was a joint effort last year between me and the plumber to get rid of the droning noise. So fully aware of what and how we did it.
 
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