Slow flow - 15mm feed Tee'd off to TWO 10mm feeds

[W4ter Boy]

Hi,

I am having some issues with my radiator heat up times on two of my radiators and I am assuming that it is a flow rate issue or something along those lines.

I have a 4 bed (large) old semi-detached house.
11 Radiators
Worcester 36CDi Compact Combi-Boiler
All my rads end up being supplied by 10mm pipe.

I have had a plumber in and he balanced everything. But still takes 45-60 mins for rads to get nice and hot. They get warm after about 20-30 mins but cold in the middle.

As per the pictures below the two in question are supplied by a 15mm pipe that is reduced to 10mm by way of a 15mm Tee with two 15-10mm reducers.

I have two questions:

1) If the feed is spit using the tee and then also reduced to 10mm all at the same point, will this have an effect on the flow and if so would there be a better way to reduce down to the 10mm?

2) Expense is not an issue and therefore would you recommend removing the 10mm and continuing straight to the rads with 15mm?


I have tried to explore several Forums and read discussions on best practices regarding 10 or 15mm pipework for central heating and it does seem to be a controversial subject.

But is 15mm better for central heating regardless of cost?


Thank you for your time advising me.

 

[Sharp Point]

Repipe your heating, microbore is absolutely pants. I flipping hate the stuff, should’ve been banned as soon as it came out

 

[W4ter Boy]

Thanks Bogrodder,
I did ask my plumber originally for 15mm but he managed to convince me that microbore would be ok... wish I had a time machine!

 

[ShaunCorbs]

Best option remove all the 10mm and use 15mm to the rads and 22 mm circuits depending on size

Copper

If plastic need to increase the dia one up

Eg 15-22
22-28 etc due to small internal bores

 

[SimonG]

It shouldn't be an issue as piped.

EXCEPT :-

Size of radiators the 10mm is feeding.

Length of run to and from the radiators.


If money is not an issue then repipe.

Or stick some cleaner in for a couple of weeks and clean it out. Maybe pull the rads off and hose on outside. Orca powerflush.

 

[Welder]

Dangerous I know, but I assume its worked fine till now.
If so, before you even consider repiping, search on here for system balancing. I will guarantee that has not been done.
Once done properly, you should notice a significant difference in system performance and response. At that point I suspect you will need to flush as recommended and then rebalance.
If that all has zero impact then, and only then, should you consider pipework changes.

 

[Pickwickpick]

Thanks Bogrodder,
I did ask my plumber originally for 15mm but he managed to convince me that microbore would be ok... wish I had a time machine!

Could be worse, could be 8mm microbore like the house I'm currently renting

But ye

Dangerous I know, but I assume its worked fine till now.
If so, before you even consider repiping, search on here for system balancing. I will guarantee that has not been done.
Once done properly, you should notice a significant difference in system performance and response. At that point I suspect you will need to flush as recommended and then rebalance.
If that all has zero impact then, and only then, should you consider pipework changes.

He's already had a plumber in who has balanced the rads, sounds like its not improved it sufficiently, so repiping and a good flush a probably in order.

 

[W4ter Boy]

Thanks everyone, system has been flushed a few times and a lot of sludge did come out, so continued until it was clear.

The rads were fitted new 2 years ago with the new comb boiler and have always been poor performing .

The rads are both large 22's 600x1800 and the microbore run is approx. 4m feed and 6m return .

Looks like I will go for the 15mm upgrade.

Many thanks again.

 

[Knappers]

I keep 10mm pipe to a minimum (just down wall) and would have used 15mm for a rad that size.
10mm pipe is fine but it has its limits