How do I flush a central heating system?

Question

My system does not have a header tank its a manual fill, you have to turn on a tap to get the system to maintain its pressure. This is not a problem but two cold radiators are see previous question. How can I put Fernnox or whatever its called into a system that doesnt have a header tap. I live in a flat.

Answer 1

If you have 2cold radiators in the system, and normal air bleeding hasn't improved it, then you have an air lock in the pipework to these rads.The easiest way to clear it is to Turn off the valves at both ends of the radiator. Now, at the end of the rad, you will have a blank plug, it is at the opposite end to the air vent. You have to remove this plug slowly to release pressure in the rad. You will get some water running out, so get some clothes and a bucket to catch any water. Now , get someone to keep an eye on the boiler water pressure for you and be ready to refill the boiler as the pressure drops. Next hold your bucket ready to catch water that will be coming out of the plughole. Open one of the rad valves slowly and catch the water in the bucket, Let the water run until it is hot. Then turn off the rad valve, and do exactly the same when you open the valve at the other end. Don't let the water run out too fast or else you will lose your pressure on the boiler quicker than it can refill. When both valves are letting through hot water, turn off the valve, and replace the plug. Then tirn on both valves and bleed any air from the rad. Keep your boiler water pressure at 1or 1 and a half bar.

Answer 2

I do not think this is a job for DIY enthusiast. You should ask your local Central Heating engineer to do it for you. This job is about 1/2 hour job per radiator and engineers may charge anything £50/ hour plus the materials (which are not too expensive) + VAT.