Have looked for a similar problem on this site but cannot find, so apologies if dealt with elsewhere!
Move into new house - built 1960s. CH system (combi) has big old rads and big steel pipes. 2 extensions were built last year by previous owner and these 2 rooms have new slimmer rads and thin copper pipes.
Problem I have is that these 2 new rads do not get hot. Plumber I know tried to balance the rads but no joy. He said that cos the old pipes were bigger the water was tempted to flow to these first so the new pipes would struggle. I do note that its not only the rad that stays cold but also the upright copper pipes.
He also suggested system needs flushing through as water in one of the new rads was black (which for some reason he couldnt do).
Does this sound plausible?? Is there actually another fault here?
I would just like to add at this time that Power Flushing would not necesarily make the joints leak. Current Flushing systems increase the flow of the water in the system, not the pressure. This, combined with cleaning fluids left in the system a few days prior to flushing and agitating the radiators as flushing is performed, often makes a difference. Costs apx £300 - £400.
A one pipe heating system, means there is only one pipe.
Most have 2 pipes, one for feeding the radiators the other for used water.
On a 1 pipe system, the heated water go thru the first radiator and then back into the same pipe, by the time the water reaches the last radiator in you home, the water is not very warm and the last radiator does heat up every well.
The affect of this is simple, you boiler could be running at full power but after the water has gone thru 5-6 radiators it would have cool down and the last ones to get the water would be slow heating up or stay cold.
On a 2-pipe system, you have 1 pipe feeding the radiators with hot water, and a second pipe taking the use water back to the boiler for reheating that is better.
one pipe system is where you effectively have one flow coming from the boiler into the first radiator. the return of that radiator then becomes the flow of the next rad in the line and so on, very common in old houses.
Needless to say not great as it is not used today (generaly). one pipe systems are a pig when adding radiators to especially with the age of the heating system. even with a single pipe system you should be able to get some heat into the new radiators.
if its a single pipe system the pipes feeding the new rads should be the same as the rest.
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