After replacing the thermostat and seeing the grotty state of the internal waterways, I decide to use Fernox F3 central heating cleaner on my classic mini.
it certainly did a far better good at removing inner crud than the holts rad flush did, thats for sure. Like I noted in the video, it even unblocked the heater matrix!
You can flush with the thermostat in place, but you run the risk of blocking at the stat if there is a lot of sediment/debris in the waterways that gets released by the action of the fernox. Some people have noted a sludge is released when this is used which will block at the stat. In my case it didn't cause sludge but lots of grit and debris.
