CH Cold Flush

Hello everyone,
I have a Ravensheat LS80 Little Star boiler where the DHW heats okay and then boiler turns off. I have been doing some research into this and have come up with replacing the DHW sensor (thermistor) I also understand that the DHW is heated through a secondary heat exchanger, so I was wondering if sludge in the system could be the cause of this? The CH has not been used for a couple of months so coincides with the DHW problem.
Does anybody think that this is a correct assumption?
I've been thinking about doing a cold water flush of my CH system (combi) by using the fill loop and turning the radiators off at the lock shield valve and flushing one at a time to the return drain point. Anybody tried this approach?
many thanks.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
Add image file
Upload 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.