Noisy radiator/balancing problems

Layout: My combi condensing boiler (Ideal HE24) is located downstairs one end of the house. There’s 22mm pipe off the boiler tee’d , one side down to 15mm to feed 2 rads downstairs total about 4kw, the other 22mm shooting off upstairs to feed the upstairs and the downstairs at the other side of the house, approx loading upstairs 5kw and remaining down stairs 4.5kw.

The 22mm runs the length of the landing upstairs approx 9m with braches off feeding upstairs and reduces down to 15mm dropping downstairs disappearing under the concrete floor (which then changes from copper to plastic) which feeds 4 rads the farthest being approx 9m in pipe at 1.5kw from this down drop.

The problem I have is to get the heat to the rads downstairs the opposite end of the house to the boiler is I have to throttle (balance) the rads closer to the boiler down via locksheild, to the extent that the rads closet to the boiler upstairs (in the bedrooms which is the worst place to have that noise) you can hear the water forcing it’s way through the lockshield valves (plus any debris flowing through the system lodges here, rattling adding to the problem).

Typically the lock shields close to the boiler are open about ½ to 1 turn. Yes we have TRVs but it’s not that end the rad the noise is coming from and it happens when the system/house is just warming.
My first thought was the pipe sizing was wrong but doing some rough calculations (using a little more info than presented here)Using temp drop of 20oc I get my index circuit (exclude boiler and rads) to around 0.56m, and my bedroom circuits to around 0.15m, as I’m relatively new to plumbing this doesn’t seem excessive??
Am I barking up the wrong tree, would hate to rip pipework out (which is not the best installed pipe layout anyhow) if I don’t have to.
Any ideas??

Presumably you have an Isar HE24. If so, the boiler output is stated for a temp differential of 15C. What made you choose 20C?

If your system was not designed for a 20C differential, e.g you have installed a new boiler into an old 11C system, you will have difficulty achieving a 20C drop.

What drop do you get at the boiler?

You say you have TRVs. There is a correct procedure for balancing systems with TRVs.

See How to Balance a CH System

yes it is an isar. 20 deg c i had from Ideal in telephone conversation with them but looking in my manual you are right with 15 deg c. I haven't used the balancing procedure you have indicated, i shall give it a go and let you know how i get on. As for rad sizing, the original boiler was non condensing but rads are slightly bigger than required anyhow, i have checked the rad size based on 70 deg c mean water temp and they are ok. I'm no expert by any stretch of the imagination so any help is greatly appreciated.
Thanks.

DavidK180 said:

As for rad sizing, the original boiler was non condensing but rads are slightly bigger than required anyhow, i have checked the rad size based on 70 deg c mean water temp and they are ok.

Click to expand...

It's not unusual to find that rads are oversized. This could be because the house is now better insulated than when they were installed, but it's usually because the installer "played safe" and installed larger than necessary.

This is a Good Thing when it comes to installing a boiler which uses a higher differential than the standard 10/11C as radiators will give off less heat when run at a higher differential and/or a lower temperature. Running at 75/55C reduces the output by 17% and running at 75/60 reduces output by 10%. You counter this by putting in rads which are 20% or 11% oversized.

When balancing, it's better to aim for consistency, i.e the same drop across all rads and the boiler. The actual temperature differential is less important, provided it is not too way out.