Number of cold radiators

[denso13]

Having had the Magnacleanse on the heating system, does it need to be flushed through with clean water before refilling and adding inhibitor

You mentioned there was some gunk in the system, so yes, better doing it.

 

[ericmark]

@denso13 has given you all the answers, however I did find my own central heating has some cold radiators when the room thermostat was preventing the system from running long enough. If the system has been running for some time, each TRV head will close, so water will be forced into radiators of cold rooms, but if, as was the case with my system, a wall thermostat turns off the pump before the TRV in warm rooms have closed, then you are relying on the settings of the lock shield valves.

Yes, closing down the valves on the first radiators to get hot, will increase the flow to areas where it doesn't. There is a complex procedure, to fully balance a system.

#3 that is spot on, and I will be the first to admit, I have not found a foolproof way that works with every system. I am only an electrician, so can only go on personal experience, I assume water from the mains has loads of air in the water, as we heat the water, air is released, so re-filling a system will mean it has air in it, and of course it also needs an inhibitor.

So one need to release the air at each radiator, and turn up the thermostat so it runs for an extended time, for the first run after messing with it. Then, even if the lock shield valves are not set spot on, the TRV heads will close radiators in turn as the rooms heat up, forcing water through other radiators.

One can get blocked pipework, had it with my sister's house, need to test both flow and return are clear, her house was a nightmare, as central heating fitted, then room partitions, so pipes ended up under the walls, but it was still clear I had a blocked pipe.