Central Heating - joining pipes of different diameter

Lemoncurd

We've been getting quotes for putting TRVs on all our radiators. The system is a microbore one and each radiator seems to have different diameter pipes going into the valve. Rather than replacing the whole system we want to have new pipework added near each radiator in order to change the valves.

Most of the plumbers have quoted for 15mm pipe to the radiators, we were assuming that the would make a join to the existing pipework near floor level. How would this join be made? can you get joints to do this and then just solder the two pipes into them?

One radiator currently has 5mm pipes and one plumber said that the only way to do this one would be to put new pipework all the way back to the manifold as you can not get 5mm pipe and refused to quote for it, is this likely to be true? We're a bit puzzled now as it sounds like he was intending to match the existing pipe diameter on each rad when adding the new pipework whereas we understood from the others that they could somehow join 15mm pipe to the existing pipework.

squiggles

Ok,im know nothing about plumbing but i have a radiator in the kitchen and that has a TRV on and mine,and all my pipework is the 5mm ones,(not to sure of the correct plumbing terms of widths of pipes) but they are as fat as a pencil.So can you not just put the TRV on your existing pipes without the hassle,or have i misunderstood your question??

Lemoncurd

Also not sure if I'm using the right terminology here but at the moment both the inlet and outlet pipes are at the same end of the radiators. I understand that in order to add the TRVs one of the pipes would need to run to the other end of the radiator in the conventional way. Also if 5mm pipe is no longer available would it be possible to get a new valve to fit? (they are leaking so need replacing anyway).

plumb1_2

Lemoncurd wrote:

Also not sure if I'm using the right terminology here but at the moment both the inlet and outlet pipes are at the same end of the radiators. I understand that in order to add the TRVs one of the pipes would need to run to the other end of the radiator in the conventional way. Also if 5mm pipe is no longer available would it be possible to get a new valve to fit? (they are leaking so need replacing anyway).

It wont be 5mm, it will be either 6/8mm or 10mm microbore.
You shouldn't need to change the pipework as you can get TRV to suite, and there is little point in changing the last couple of feet to 15mm, the rad wont work any better.
And the plumber is correct if you want to change to 15mm it is best to go back to the manifold.
With the pipes entering at 1 side of the rad, you have Yorkshire Valve 8mm (if i recall, but could be 6) both flow and return to single valve . They have a injector pipe 150mm inside the valve.
You will have to take these out a repipe to either side of the rad.
The best case tbh would be to repipe,take out the manifold and connect with tees,I would recomend you use 10mm or 15 mm

StephenB_2

4, 5, 6 mm copper pipe at https://www.bes.ltd.uk

Search for copper and take the first hit (http://www.bes.ltd.uk/products/139.asp)

SJB

plumb1_2

StephenB wrote:

4, 5, 6 mm copper pipe at www.bes.ltd.uk

Search for copper and take the first hit (http://www.bes.ltd.uk/products/139.asp)

SJB

4,5,6mm is only used for Air-Con and refridgeration work, thick wall as it has to be brazed, higher working pressures.

StephenB_2

plumb1 wrote:

4,5,6mm is only used for Air-Con and refridgeration work, thick wall as it has to be brazed, higher working pressures.

I will take your word for it; I'm just a simple soul with a google search engine. No 'd' in refrigeration

SJB

Lemoncurd

plumb1 wrote:

It wont be 5mm, it will be either 6/8mm or 10mm microbore.
You shouldn't need to change the pipework as you can get TRV to suite, and there is little point in changing the last couple of feet to 15mm, the rad wont work any better.
And the plumber is correct if you want to change to 15mm it is best to go back to the manifold.

Honestly, it really is 5mm - we have a mix of 5mm, 6mm, 8 mm and 10mm! it seems that every rad is different. We have measured it and so have the plumbers. I know ideally we should replace the lot but downstairs all the pipework is under concrete with wood mosaic flooring over the top and we certainly don't want to get all that up unless we have to and there isn't an easy alternative way of routing new pipes. We're really looking for the best quick fix in order to get TRVs in place.

plumb1_2

Lemoncurd wrote:

Honestly, it really is 5mm - we have a mix of 5mm, 6mm, 8 mm and 10mm! it seems that every rad is different. We have measured it and so have the plumbers. I know ideally we should replace the lot but downstairs all the pipework is under concrete with wood mosaic flooring over the top and we certainly don't want to get all that up unless we have to and there isn't an easy alternative way of routing new pipes. We're really looking for the best quick fix in order to get TRVs in place.

In over 30yrs( i know iam old:D ) i have never seen 5mm pipe fitted to a heating system, 6mm yes, and not often
as you said the pipes go into 1 valve, yorkshire valve 6/8mm, but i think they are 8mm.
you can always drop feed the rads from upstairs in 10 mm in plastic cladding 30x12mm