Regarding the loft CH piping. As I have explained, a 15mm copper supply and return were added to the end of the 1st floor CH circuit and the top of these pipes look like this in the loft:
The 15mm feed is immediately tee'd and the runs to the left go to the supply and return valves on one of the radiators (this one never gets warm). The run to the right is almost immediately tee'd again.
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This is the second tee. The shorter supply and return go to another radiator, the closest to the loft feed and this radiator gets warm, but never hot. The run to the right goes to the bathroom towel rail. With the towel rail, the supply pipe gets warm, but the towel rail itself never heats up and so the rail and the return are always cold. I wonder if the supply valve is actually blocked.
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So, the above two photos show the "star" style of piping, which I assume was done to minimise the length of pipe required i.e. two pipes (supply and return) from a central point to each radiator/towel rail.
Under the floor boards, the plastic pipe is connected to copper tails that connect to the radiators:
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My understand of "normal" CH piping is that both the supply and return is run to each radiator in turn, with a tee off each to the radiator supply and return valves. With correct balancing, this ensures each radiator gets a feed of hot water, so the radiators closer to the pump/boiler would have a lockshield valve that was barely open and those furthest from the pump/boiler would be fully open.
After the last radiator, the return pipe makes its way back to the boiler, so I assume the pump is responsible for not only supplying hot water to each radiator, but also forcing the cooler water back to the boiler. Is this also compromised by the "star" shaped piping in the loft?
Here's a diagram that reflects my understanding of "normal" CH piping, although this one doesn't show the different 22mm feeds to the ground and 1st floor, splitting into 15mm feeds to the radiators:
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To me, this star shaped piping in the loft means that a 15mm feed is instantly split into 3, so the flow will be reduced and there is the chance of the flow being stronger to one of the radiators than the others, which over time would allow silt from the radiators to clog the pipes as there wouldn't be sufficient flow to remove it.
Is this a fair analysis of what might be happening in the loft or am I completely wrong?
As well as replacing the 15mm pipes to the loft with 22mm pipes, taken from the existing 1st floor 22mm feed, is there any benefit to changing the run of the pipes in the loft?