adding bigger pipes to 8mm system

jl81 · 10 Nov 2019

hey,
we have a pressurised microbore 8mm system and combi boiler - for 90% of the house - perfect all piping hot.

1 radiator (1.4mx50cm double) gets warm-ish and stone cold at bottom. there dosent seem to be any restriction to flow with the radiator off and the system has been cleaned. Thinking we need to seal off the possibly kinked/too small pipes (yay sealed in plaster). and upgrade to 10 or 15mm pipework for this one radiator.

2 questions
1 - is the radiator too big for the pipework

2 - had a couple of guys look at the job all bar one said doable - but pipe should be fine (want to 'clean' first - which we have tried) one stated that pipe is too small but adding larger pipes to 1 or 2 radiators could screw the rest of the system up and stop it working. Is he right?

just wish there was a general consensus on the issue/solution

muggles · 10 Nov 2019

Does that radiator work if you turn all the others off?

Iamchamps · 10 Nov 2019

Could just be a balancing issue.

jl81 · 10 Nov 2019

muggles said:
Does that radiator work if you turn all the others off?

a hair better if anything.
rad is 2.4kw btw.

& tried balancing also nope. all are dialled down, this is wide open with hot inlet stone cold return, - and no obvious restricted flow on either.

muggles · 11 Nov 2019

Sounds like a blockage to me. Turn off the radiator valves and remove the radiator from the wall. Adapt a hosepipe so that it will fit onto a valve, run it outside then turn the valve on, see whether water flows freely. Repeat with the second valve

jl81 · 11 Nov 2019

muggles said:
Sounds like a blockage to me. Turn off the radiator valves and remove the radiator from the wall. Adapt a hosepipe so that it will fit onto a valve, run it outside then turn the valve on, see whether water flows freely. Repeat with the second valve

Tried and it flows fine & crystal clear.

alan999 · 11 Nov 2019

Has the radiator ever been really hot

Killalot · 11 Nov 2019

I had the same problem with both radiators in the conservatory I changed the pipe to 15mm had to leave about 1m off 8mm pipe because it was in the wall. Works fine now.

jl81 · 11 Nov 2019

alan999 said:
Has the radiator ever been really hot

No.
No matter what we did. It’s 2.4kw. Which is why I’m wondering if it’s too big for 8mm.

alan999 · 11 Nov 2019

Possibly. If the radiator is already off and you are confident enough you could try fitting a length of pipe across the 2 valves. See if that heats up or not.

Terrywookfit · 11 Nov 2019

Is this copper pipe how long is the run of 8mm + any elbows ??

John D v2.0 · 11 Nov 2019

jl81 said:
No.
No matter what we did. It’s 2.4kw. Which is why I’m wondering if it’s too big for 8mm.

You can get a lot of heat through 8mm especially if the temperature drop is designed to be 20c or more but if the pump doesn't have enough oomph for the length it might not flow well

jl81 · 11 Nov 2019

alan999 said:
Possibly. If the radiator is already off and you are confident enough you could try fitting a length of pipe across the 2 valves. See if that heats up or not.

Sorry it gets warm. We know heat is getting there and with the radiator off there isn’t any restricted flow from either pipe that we can see.
Starting to wonder if giving a chemical clean might be an idea.

jl81 · 11 Nov 2019

Terrywookfit said:
Is this copper pipe how long is the run of 8mm + any elbows ??

Not 100% sure. Hunks are encased in plaster
Think maybe 8-10m from manifold.

John D v2.0 said:
You can get a lot of great through 8mm but if the pump doesn't have enough oomph for the length it might not flow well

Wouldn’t that flag on other radiators as well though? It’s just this one that’s a pain.

John D v2.0 · 11 Nov 2019

jl81 said:
Not 100% sure. Hunks are encased in plaster
Think maybe 8-10m from manifold.

Wouldn’t that flag on other radiators as well though? It’s just this one that’s a pain.

8 to 10msa lot, as that's at least double that for flow and return.
I did the calculations for a new cavity wall bedroom and decided it was ok on a basic 3m head pump with 5m each way, that was similar pipe, 10mm speedfit with no joints. So having double that, assuming it's all 8mm copper would be a challenge.
Are the other rads similar distances on 8mm too and similar sized?

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adding bigger pipes to 8mm system

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