I've put some Fernox superconcentrate F1 in one of the rads and its been circulating for about a month or more now. So now I want to flush the CH system out. I'm struggling to find a definitive way to do this online? As soon as its mentioned its a sealed system (Combi) everyone says consult a heating engineer? Do I just open the drain to allow it to run out and the connect the filling loop and turn it on? I assume I'll need to bleed the combi afterwards etc?

Dave., November 2008

Not a definitive answer but in short this may help.

Ensure combi is off/cold. Open all rad valves and drain system at lowest point. Opening rad vents as you go (starting upstairs) speeds up draining off process.

Once system is drained down close off drain point and close rad vents. Refill system and vent air from rads. As you remove the air from each rad in the system you need to repressurise system by continually topping it up via the filling loop. Check water pressure gauge on boiler ensuring you dont pressurise system over one and a quarter bar.

System now requires flushing out of all added cleansing chemicals. Do this by following the above paragraph at least once. When completed your system now requires an inhibitor/protector - add this during your final flush before system has filled completely (use protector as described in manuftrs instrs).

Again make sure all rads are vented and system pressure is set at one or one and a qrt bar and disconnect fill loop. (You may also need to vent your heating pump at your boiler).

There is more work to this than meets the eye especially in the correct order hence people advising you to get a htg engr. To clean/flush an system properly Power Flushing is recommended. There maybe plumbers in your area how provide this service - prices vary but start from about £200 upwards. But if you follow the above suggestions you should be able to do this. However depending on severity of rad cold spots this may not be sufficient enough to cleanse/flush your system properly.

NB Sender cannot accept any responsibility this is why a qualified htg engr is recommended. Always follow manftrs instrs.

stevie t, December 2009