8mm microbore and new rads

[LeonR]

Hi all,

Soon I plan to start replacing some radiators and they are currently all connected on an 8mm microbore system where both pipes go in the same end/valve.

I'm pretty sure that these valves are hard to get now, so it makes sense to change them before one of them breaks?

What would you recommend when fitting new radiators?
Shall I use an 8/10mm TRV at one end and then use a compression fitting on the other pipe and extend the microbore to the other end of the radiator? What fitting would I use at the opposite end?

Is this generally what people do or would they convert it to a larger bore under the floor boards and then fit with the more traditional look? (15mm etc)

I assume it makes sense to add a TRV rather than just a twisty valve?


I'm not sure what the done thing is, although I think I can do it with some advice on what to buy.


Cheers,
Leon

 

[lame plumber]

bin the micro bore and up to 15mm/22mm would be my choice.

 

[LeonR]

Not sure I can do that easily to be honest, it did cross my mind though.
It may be possible upstairs, but not downstairs (flooring).

To be honest, apart from it looking a bit pants it's been working ok so far.

I'm guessing it's a bad idea to start mixing it up (8mm and 15mm) as it probably unbalances it?

 

[lame plumber]

if you want all your nice new rads to work having messing around with the system, disturbing the crud......

 

[LeonR]

Yeh, i've put cleaner in it today to at least make an effort to clean it out as best as I can, i've never looked inside a pipe which has been in use since 1970 so I don't know how much crud builds up to be honest.

I know the radiators are colder at the bottom so clearly that's not a good sign.

 

[LeonR]

So under the assumption that we keep the microbore does anybody have any advice for TRV and connections etc?

Cheers,
Leon

 

[Best]

You need to have a TRV valve on one side of rad and a lockshield valve on the other.
The lockshields are just normally same as a wheel head valve but have a tamper proof head.
Usually where you have no choice but to join onto Microbore it is neater and better to use a soldered fitting - (elbow or whatever.)
It will unbalance the system if you increase some of the pipework to 15mm, but that can be fixed by balancing it all carefully.
You are better to get a heating engineer to do it, if you know a good engineer, and I would agree with ripping as much as possible out, if not everything.

 

[Best]

One other point, - if you are just doing a room or two and replace the 8mm with 15mm as far back as you can go at that particular time, it will help the flow to rad because the pipe will have less resistance.
Frankly, old dirty rads and 8mm Microbore are best replaced sooner or later. I wouldn't waste any time or money on working on them

 

[SmokeyJ]

Fit trv's on all radiators apart from one closest to room stat.
Running 15mm for 1m or so won't have much benefit with existing supplies being 8mm, it certainly won't have any negative effects. I personally just cut the microbore as far back as possible and convert to 15mm.
Either way convert to 15 and small length of 15 pipe or extend the 8mm and convert at rad valve with reducing set in valve..
Any merchants will be able to tell you what fittings you need providing you know sizes. Prefer to solder over compression as it's neater and especially if converting under floor.

 

[Best]

Fit trv's on all radiators apart from one closest to room stat.
Running 15mm for 1m or so won't have much benefit with existing supplies being 8mm, it certainly won't have any negative effects. I personally just cut the microbore as far back as possible and convert to 15mm.
Either way convert to 15 and small length of 15 pipe or extend the 8mm and convert at rad valve with reducing set in valve..
Any merchants will be able to tell you what fittings you need providing you know sizes. Prefer to solder over compression as it's neater and especially if converting under floor.

Yes I agree, for to just put 15mm from new rad and down through the floor a metre would be cosmetic only, although also means the 15mm copper is hard copper more suitable for compression rad valve.
But removing a substantial run of 8mm and replacing it with 15mm will make a massive difference to flow to rad. I always look at it that even in a small room the Microbore will often have several metres to go to flow valve and then same again to return. So usually the Microbore is too long and the rads will not perform well, especially in colder weather.

 

[LeonR]

Ok thanks guys, I appreciate the help!

I could probably change all of upstairs to 15mm over time to be honest, I won't be able to do downstairs though due to the way the pipes are under the flooring.

As I would have to change the rad's over time, how do I tackle this? I know it sounds like a daft question but would I have to solder in a T peice and put a 15mm manifold off of that? (and keep the current 8mm manifolds in place until i've replaced them all?)

I think I could do the work (logically minded/experienced with most tools) I just need to be sure i'm doing it with 'best practice' in mind and not bodging it.

So just to clarify, it's ok to run all of the upstairs on 15mm and leave downstairs on 8mm?
Would I not have to limit the flow on the 15mm rads? Otherwise i'm guessing the 'easiest route' would be through all of the new 15mm pipework which would result in less pressure on the 8mm downstairs?

I know this is probably ABC stuff so apologies for that.

Cheers,
Leon

 

[Best]

Yes, the 15mm will be easier route for flow but that is what the lockshield valves are partly for.
You will find the rads on 15mm will always work better though anyhow in many heating system designs

 

[LeonR]

Ok cool, i've attached a picture of the 2 manifolds under the floor.



What's the best way to get 15mm manifolds on the same pipe? Would you put a T in before the 8mm manifold and take a 15mm manifold from that new T piece?

Edit: the pipe is 15mm that goes in to the manifold (not in the pic though).

Thanks,
Leon

 

[Best]

Just depends Leon what way it is all piped. Ideally I would go to tee off where the pipes are 22mm, but it would be okay to tee off the 15mm as you are not actually adding a radiator to the circuit.
Whatever you choose to do, try to install any new work that is fairly substantial, in a proper way that would suit if the rest of the system was renewed.

 

[LeonR]

Ok thanks for the advice, are there premade 15mm manifolds available or do I just make it up with T joins ?

Thanks!

 

[WHPES]

If it's not already been mentioned, you need a differential bypass valve fitting between the outlet of the circulation pump (assuming it's on the flow side) and the return to the boiler.

 

[LeonR]

Would that not already be there? (Confused!)

Thanks,
Leon