This Ravenheat CSI 120 has been suffering with hot water problems. Hot water from the tap was fluctuating between hot and lukewarm. The reason for that was a blocked secondary heat exchanger. I have cleaned this exchanger about 3 months ago and suggested to the client that the system should be flushed to avoid the heat exchanger blocking again. The boiler has TF1 magnetic filter fitted on the return, but it seems that on very dirty systems it is not an adequate protection.
The course of action was to clean the system using suitable chemicals and Adey Magnacleanse system connected to return pipework to the boiler in place of TF1 filter. I prefer Adey Magnacleanse to power flushing as I find it more effective and quicker to do. You can read more about this system at Adey web site: Magnacleanse System. Below some pictures of sludge removed from the central heating. I like to clean the filters a few times during flushing to make sure they are more effective. This is what I got from about 2-3 radiators on this central heating system.
System got flushed and protected with suitable inhibitors (Sentinel X100). Once I got a nice and clean system water I cleaned and refitted TF1 filter and isolated the boiler. I then removed hot water heat exchanger to inspect it. As I suspected it was badly blocked on system water side. See picture below. The blocked port is on the right hand side and you can clearly see the blockage.
Next picture shows what comes out of a blocked heat exchanger if you tap it to remove the blockage. Please note that this is only a small part of blockage material that came out. I do not think it is possible to fully unblock a plate heat exchanger by tapping it alone. The best solution would be to replace it with a new one to avoid call backs. There are different methods of cleaning them with spirit of salts being the most popular one.