Vaillant ecoTec plus droning noise only on DHW

[gjspg]

I have a 3 year old ecoTec plus 831 that is working perfectly ok for CH but when DHW is called for the boiler has started to make a loud droning noise that appears to come from the top of the boiler around the main heat exchanger. It is nearly 3 yrs old and has had a new pump fitted, due to a collapsed bearing, when 2yrs and 3 months old. The system was not powerflushed by the installer as he considered the CH system to be reasonably clean when fitted. When the pump was changed I got him to fit a Magnaclean to the system and after the initial collection of debris is now only collecting very small amount of silt. The system has two cartons of inhibitor.
We started to hear this droning about a month ago and if anything it is getting worse. When you call for DHW and turn the hot tap on for full demand the diverter valve moves fully over and after the usual delay while the boiler checks for the rate of flow as it turns the gas to full demand and the fan goes to peak gas/air mixture after a couple of seconds you can hear an aircraft type droning starting to appear that gradually gets louder. If you turn the hot tap down and reduce the demand the boiler ramps down on the fan speed as you would expect and the sound reduces. Now you might say that it must be the fan bearings causing the noise when on full speed but the sound does not seen to be coming from that area of the boiler it seems to be coming from the top were the main burner heat exchanger is. By the way the DHW is always hot there is no alternating hot and cold like some posts have problems with. Any thoughts please.

 

[gas4you]

This will be system muck settled in the bottom of the heat exchanger coils.

A very common problem with Gianoni heat exchangers.

Isolate the boiler from the system and reverse flush the HE out, turning on the hot tap as well to clean through the 'sump' called the plate HE.

 

[gjspg]

Hello Dave
Thanks for replying. I follow what you say so is the blockage more likely in the main burner HE or the smaller plate HE at the bottom of the cabinet. possibly both I suppose, although I thought I had a reasonably clean system.
Also if it was the main HE would it not also make a noise when the boiler starts up from cold and the CH calls for heat and the control board puts it in full gas burn to bring up the temperature. One other peice of info in that regard, I know the installer "ranged " the boiler down from it's maximum 24kW to 20kW because it's a 12 rad system. Would this mean that the boiler does not run at full bore during warm up for CH as it does for full demand for DHW?.

 

[icewinder]

I have a 3 year old ecoTec plus 831 that is working perfectly ok for CH but when DHW is called for the boiler has started to make a loud droning noise that appears to come from the top of the boiler around the main heat exchanger. It is nearly 3 yrs old and has had a new pump fitted, due to a collapsed bearing, when 2yrs and 3 months old. The system was not powerflushed by the installer as he considered the CH system to be reasonably clean when fitted. When the pump was changed I got him to fit a Magnaclean to the system and after the initial collection of debris is now only collecting very small amount of silt. The system has two cartons of inhibitor.
We started to hear this droning about a month ago and if anything it is getting worse. When you call for DHW and turn the hot tap on for full demand the diverter valve moves fully over and after the usual delay while the boiler checks for the rate of flow as it turns the gas to full demand and the fan goes to peak gas/air mixture after a couple of seconds you can hear an aircraft type droning starting to appear that gradually gets louder. If you turn the hot tap down and reduce the demand the boiler ramps down on the fan speed as you would expect and the sound reduces. Now you might say that it must be the fan bearings causing the noise when on full speed but the sound does not seen to be coming from that area of the boiler it seems to be coming from the top were the main burner heat exchanger is. By the way the DHW is always hot there is no alternating hot and cold like some posts have problems with. Any thoughts please.

I see the post is 3 yrs old but my combi boiler problem is incidental to yours (A Vaillant ecotec plus 837).
Did you suss it bud ?

 

[Agile]

I suspect he had it cleaned and hope that it solved the problem.

That heat exchanger has several coils in parallel and it can be difficult to clean them if partially blocked because the cleansing flow bypasses the blocked tube to take the easier route.

Tony

 

[gjspg]

Hello Icewinder
Yes I did get it sorted. I got the installer back and he isolated the boiler and flushed both HE. At the time it was very difficult to be certain exactly where the noise was emanating from. Tried the old engineers trick with the long screwdriver to the ear but not successful.
I will add that this occurred when it was winter time and the incoming mains temp. was a few degrees lower and the boiler was being asked to supply DHW at high flow rate to a bath. When asked to supply normal sink or shower demand the flow rate was never high enough to bring the droning on.
Hope this helps.

 

[icewinder]

Hello Icewinder
Yes I did get it sorted. I got the installer back and he isolated the boiler and flushed both HE. At the time it was very difficult to be certain exactly where the noise was emanating from. Tried the old engineers trick with the long screwdriver to the ear but not successful.
I will add that this occurred when it was winter time and the incoming mains temp. was a few degrees lower and the boiler was being asked to supply DHW at high flow rate to a bath. When asked to supply normal sink or shower demand the flow rate was never high enough to bring the droning on.
Hope this helps.

thanks for the reply, after further diggin around for more info I have also been told it could be crud block causing the problem or undergassed.

Someone else did say that the noise can also happen because it's battling to stay alight and the gas/air ratio is completely messed up.
The noise can also be caused with the corrugated tube leading to the gas valve been restricted with the dreaded black dust.
Can anyone confirm that this might also be the problem ?

 

[Bunnyman]

Nope main ht exch as in previous posts its a common problem an is dirt that has settled in the coils, can be a pig to shift

 

[Shirty]

Yes had a couple now with these heat exchangers just on hw

 

[Terry lambert]

I went to service An 831 the other day making a racket on hot water.

Adjusted the air/gas ratio which was out, and it was sorted.

Also had it on an 837 with muck in the hex

Bunnyman is the kiddie on these though, hence the name

 

[icewinder]

OK thanks fella's , can the muck normally be cleaned out the ht exch ? if not how much are we roughly talking ? ball park figure to put right ?.

 

[Agile]

Adjust air/gas ratio £100

Chemically flush/clean main HE £300