Venting heating pipes in bungalow roof

Help! I am thinking of installing a new heting system which will mean fitting all the pipes in the loft of my bungalow and dropping the pipes to the radiators in the rooms below The curent pipes are in the concrete floor and are completly shot Will this cause venting/airlock problems? if so, what can i do to stop the problems I intend to use a combi boiler
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The only advise I'd give you, is to make sure that you can bleed all the air out from a large bore pipe on the flow of the heating system, and make sure it is above the height of the boiler. Because the boiler will be above all the radiators, you need something which let all the air out above the highest point of all the appliances in the system. Something like a stopcock on the flow side of the heating pipework will do, and make sure you can bleed it till water flows from it. This will let the system gather any air it may produce all to one point ready for it to be blown out.
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Where is the boiler to be installed? Will it be a sealed, pressurised circuit?
Assuming the boiler is going on the ground floor and is sealed, you should have no troubles at all.
However, you must ensure there is a method to bleed the pipes in the loft space. What I would do is run the pipes not quite horizontally in the loft, but rising to a point. The rise can be very, very slight. Then, at the peak, install a vertical stub of pipework from both flow and return and cap with automatic bleed valves. Leave these valves open for a week after you refill the system. Design the pipe runs so that the rising air will always find its way to the automatic bleed valve. You can still tree off, rather than snake around if this is borne in mind.
If the boiler is installed in the loft, with the pipes in the loft floor below the level of the boiler, there will probably be an automatic bleed valve in the boiler. If so, this should be able to deal with it without additional valves.
Christian.
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