Replacing radiator branch with microbore

What pressure is your pump running at..?

It's a Grundfos pump currently set on the 'II' mode which I think is constant speed. 'I' doesn't get the heat to the furthest rads and 'III' is too noisy. There are also two constant pressure modes but having accidentally set it to that in the past and not having great results heating engineer recommended to use the currently set value (on the basis "that's what I usually set").

Silent Ice snipped-for-privacy@example.null wrote in news:v5r7e3$erq4$ snipped-for-privacy@dont-email.me:

I was going to query the pump setting too but it seems you have taken a logical approach. I assume that the distant rads that are problematic have their lockshields fully open?

My guess is that your well locked down one is both small and very close to the boiler/pump end? And what drop are you trying to achieve? If it is a small rad then you are unlikely to get the recommended system drop but I wouldn't put too much emphasis on that. Having a small rad on at

On restricting the flow with a section of microbore, I'd say that was worth a punt, that is if pipe length (inc flow & return) is 2m or more, less and I wouldn't expect much difference. I'd keep 15mm rad tails for aesthetics then convert to 10 or even 8 under the floor. I have used

Yeah they've been left open, I think part of the problem is they are also recent additions and I sized them based on a calculator. With hindsight, the rest of the house is oversized and so the newer ones struggle compared to the rest of the house and should have been plus sized as well.

From the pump there's about 2.5-3m of pipework to the branch off and it's the first on the run. A type 22 it's narrow but fairly tall approx

Unfortunately it's a very short run, the main trunk runs under the landing floor and it's a corridor so everything branches off from this, so there's probably 30-40cm to this particular radiator and same for the bathroom. The other radiators are off longer branches (some much more). If using thinner pipe might not work to restrict flow to the first radiators then there might be an optimisation with the pipework of the furthest to think about.

Didn't think about blocking being a problem. We don't have a magnetite filter, it's not easy to find a suitable place to fit but have considered it and had a quote done 18 months ago but didn't go ahead.

Silent Ice snipped-for-privacy@example.null wrote in news:v5ttv3$10slr$ snipped-for-privacy@dont-email.me:

I have done it using the feel of the pipes by hand but as you are having problems it may be worth the effort. As I have the bits (IR them 15quid) I always do it high tech now. Useful too to note if you have dramatic reductions in the flow temp at distant locations, you shouldn't.

Also, perhaps better to balance output and rely on your TRVs to cap that off when the room comes to temp. By all means throttle down hugely oversized rads later if you feel they are 'hogging' the boiler's output.

I only thought of this after posting but why not artificially lengthen that run by having a moderate coil of plastic microbore under the floor when you remake that connection? Plastic as its ID is smaller than copper and heatloss lower (wrap the coil in fibreglass to keep the heat where you want it). 10mm plastic microbore is about 40quid for a 25m length.

Highly recommended if you can find a spot and it really is a straightforward DIY job. It can go on flow or return, anywhere on the main trunk.

The flow through the 8mm pipe will be ~2.5 times less than 15mm pipe and that will restrict the total flow of hot water. Why would you want to put in a flow restrictor..?

Because the flow restrictor that he has is noisy, and it's needed to get the system balanced to the point where the last rads get warm.

Having a longe length of 8 mm *should* be less noisy that the single point of a valve turned down to "almost nothing"...

Thomas Prufer

On 15mm pipework, my 10 radiator system is totally silent, each radiator is fed from a manifold made up of