Boiler banging ..EcoMax Pro 28E

[smallbore]

In July someone reported here that their boiler banged, but only when they turned the HW temperature up. There didn't appear to find a solution but, as my EcoMax Pro on a microbore system does the same with CH, not HW, I thought I'd see if someone had any suggestions.
Heating HW produces no banging. On CH when the temperature's set to 59 or lower there's no banging. A little higher and you get a short series of repeated bangs and a bit higher there's a longer series. At 70 there's a few each second. You can feel it in the pipework. The amount of banging follows the modulation level but a few years ago it operated noiselessly at 75.
The boiler's been serviced with no fault found and the circulation pump's been changed for a higher head one which made no difference.
Is it possible that the TRVs are getting gunged up so water's not getting out of the boiler fast enough? HW's ok but that's got a really low resistance to flow.
Would a bypass valve do any good?
Now the weather's cold 59 is very noticeable!

 

[jtsplumbing]

If your in a hard water area it could be scale build up in heat exchanger or dirty system.

 

[king of pipes]

As above your heat exchanger is partially blocked sentinal x400 added to the system and left for a week in the system may help break it up and a mag filter to catch any debris then a power flush . cheers kop.

 

[jtsplumbing]

As above your heat exchanger is partially blocked sentinal x400 added to the system and left for a week in the system may help break it up and a mag filter to catch any debris then a power flush . cheers kop.

Only thing is I don't like Sentinel products ! always been a Fernox man.

 

[smallbore]

Thanks for the suggestions! Although this is a hard water area the water softener takes care of it and, when a flange for a power shower was added to the hot water cylinder, there was almost no deposit in it.
The header tank had a maintenance solution added 2 years ago but I didn't note which one. When the system was drained a month ago to check its condition the water was very clear. X200 was added to see if it reduced the noise, but it didn't make any difference at all.
I know this doesn't eliminate the heat exchanger, unfortunately!
What made me think about flow rate was that the HW temp can be upped to 80 with no noise, but with CH selected 59 is max!

 

[king of pipes]

You are geting confused its the other way round heating 80 degrees , hot water 60 degrees. There is a restriction there fact you need a engineer to sort it out . regards Kop

 

[smallbore]

I put that badly!
With the boiler output temp set to 80 and only HW demanded the boiler's quiet. The h/w cylinder stat is set at 70.
With CH selected banging starts as the output temp rises above 59. So I have now set it to 59.
The banging is very rhythmic with 3 - 4 bangs/second which increase in loudness from little taps to something hitting the casework as the output temp climbs. It comes in batches of 5 to 20 seconds.