Boiler noise


Got a Bosch Worcester combi 12 year old boiler on a 8 radiator system. Just replaced the kitchen radiator with a larger one, flushed the system several times but now when running the hot water the boiler is making a rumbling noise. I'm thinking the system needs dosing with Fernox but after looking at the Screwfix site I'm at a loss at choosing the right one. Which one should I go for?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Maybe air in the system. Has everything being bled?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I cannot see how putting Fernox in the CH part of a combi will help reduce noise in the HW setup. You do of course need to put inhibitor in the CH system when you have flushed it out to prevent corrosion.
Adam
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Yes it has. I'm going to try Fernox noise reducer next. I've been told that will help.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.