Is it necessary to clear the old residue from the old radiator before installing a new combi boiler

Hi Neil, in my opinion when a new boiler is fitted, it usually is standard practice to flush the system to remove any sediment or sludge from the system to try and protect the new boiler as much as possible. Power flushing the system is the ideal solution but as stated above it malfunctioned but there are other ways in doing so. when the new boil boiler was fitted was there a magna clean installed ? and i can only assume inhibitor was put into the system, if this was done without system being cleaned out it will pretty much be worthless until any sludge or sediment is removed. you can shutdown both ends of rad valve/s in question and disconnect and manually clean individually with a hose in garden also make sure to agitate rad with a vibra clean or a white rubber mallet. if you are not overly confident i would recommend finding someone who could do this for you. but 100% the more sediment and sludge you can remove from the system the better, not only help prolong life of boiler but will be more efficient. hope this helps. Mike.

the system should have been properly power flushed before new boiler was installed, and magnetic filter installed in return pipework next to boiler, should you now have problems with residue in the boiler components you may find that the boiler manufacturer may not honour the boiler guarantee.

Your boiler installation manual will stipulate that primary water, within the system, must meet the standards as set out in BS 7593:2019. This is part of the commissioning process and should be documented on the benchmark certificate, within the manufacturer's instructions, and left with the user. There are various methods by which the system water can be treated, until it meets these standards, and testing kits available, to confirm its condition. Dirty system water is the biggest cause of system and boiler breakdowns and premature appliance mortality, as well as decreasing efficiency, burning more fuel and increasing emissions - which is why it is now regulated by Part L of the building regulations. If you need to call out the manufacturer under warranty, they may void your cover if the water does not meet the standards. This is important for ongoing maintenance, throughout the warranty period, as well as installation and commissioning. Hope this helps.

There is two types of flushing. Chemical flush and a power flush / magnacleanse. A chemical flush is usually done after installing the boiler you run the chemical through for an hour then drain it all down. Run clean water through for abit then add inhibitor to the system. This is recommended by all boiler manufacturers. A power flush / magnacleanse is a much better option although usually more expensive. You isolate each radiator and agitate the sludge inside the radiator and dump out the mucky water. It doesn't sound like the installer has done either of these flushes. Hope this helps