draining down combi boiler system then refilling

IM just about to add a few new radiators on to my existing CH circuit. im about to drain the system. my boiler is a 24i junior WORCESTER BOSCH. the general advice seems to be that this a fairly straightforward task and shouldnt provide a competent diyer with too many problems . ive read all the literature i can find but any experiences /advice or tips would be really useful also any advice on refilling would be welcome.
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IM just about to add a few new radiators on to my existing CH circuit. im about to drain the system. my boiler is a 24i junior WORCESTER BOSCH. the general advice seems to be that this a fairly straightforward task and shouldnt provide a competent diyer with too many problems . ive read all the literature i can find but any experiences /advice or tips would be really useful also any advice on refilling would be welcome.
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1. When draining, do it when the water is still warm. It seems to remove more crud that way. Consider putting in a flushing chemical a day or two before starting work. (You may need to drain down once before putting in the chemical and then drain down again when you are ready to start).
2. Use a hose attached to the drain point and lead it out of a nearby window to an outside drain gully. It doesn't matter if it goes up first. Provided there is a good airtight join and the hose goes down again afterwards, the hose will syphon out down to the level of the drain valve, not the window ledge. Don't try to use containers unless absolutely necessary. There's a lot of water in your heating system.
3. Look carefully at the water colour. If it is a nice golden colour with no flakes (i.e. think urine) then it is in excellent condition. If it is pitch black with big chunks, you have a corrosion problem and should flush your system thoroughly before installing the new radiators.
4. When it is drained down, take the time to insert an additive filler point at a reasonably high point in the circuit. This is just a T with a short vertical pipe ending in an isolation valve and some more pipe. When you want to add chemicals to the system, rather than squirting expensive chemicals into your face by accident using a syringe contraption, you can use the cheap non-concentrated form by opening the valve and pouring into a funnel. The parts to do it are cheap and you'll make your money back the first time you do it!
5. Install drainable lockshield valves. Although maybe not quite so attractive they aren't too bad. They make removing radiators one at a time really easy and mess free. You'll never need to mess up an otherwise good painting/papering job again as you try to squeeze your brush and hand behind the radiator. You can remove the radiator in no time with just a bucket and a couple of plastic bags (WITHOUT child safety holes!) tied over the tails. No need to drain down the entire system, or disconnect one end of the radiator as the water runs down the supply pipe and pours onto your carpet.
6. Some installers recommend that you don't install inhibitor after you have finished. This is because replacing radiators that have corroded through is a lucrative business opportunity for them. They would also recommend that you smash your boiler with a baseball bat every couple of years if they thought they could get away with it.
7. If the new radiators are in a new section of house, or a conservatory, or other part that might benefit from independent control, consider subzoning your system so that they can be controlled and timed independently from the rest of the house. I prefer to have at least one zone per floor. I particularly like not having to heat bedrooms during the day without labouriously going around turning them off manually.
Christian.
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