Brand new heating system

[Agile]

Your boiler probably has a setting which adjusts the heat input for the central heating. Has that been checked?

There could also be a problem with the gas pressure at the boiler input.

I have had a look at the boiler details. It is a new design and has some slightly unusual features.

It does not have a maximum power setting adjustment. So it can deliver between 6 kW and 27 kW of heating power at a flow temperature of 50 C. it automatically adjusts the power required to reach the flow temperature that you set yourself on the front knob.

The temperature control knob can set the output temperature right up to 80 C. But the efficiency goes down a lot if you set it above 70 C as it will not condense and thus lose about 12% efficiency.

The latest standard for sizing radiators is based on a flow temperature of 50 C as that is as high as heat pumps might give. At a flow temperature of 70 C the heat output will be higher.

Radiators will always be hotter at the top as the hotter water is less dense. That is totally normal. Lower down they will be slightly cooler depending on how they have been balanced. With a condensing boiler it is best to set them for a differential of about 15 C to 20 C as that encourages more condensing and thus higher efficiency.

Balancing is quite time consuming and is best learnt by doing it. I know a few tricks by first presetting typical lockshield positions according to the radiator size and distance from the boiler. Sometimes I can reach acceptable balance just by that. But that assumes all the lockshields are the same design and the pipework correctly sized.

 

[MeldrewsMate]

OP, you have stated that two problem radiators improved when the upstairs TRVs were turned off, however you also stated that two towel rails stayed hot even though they were turned off too.
First you must make sure that each towel rail is off, or at least so flow restricted that the incoming pipe temperature is SIGNIFICANTLY hotter than its outlet pipe.
Secondly you must wait at least 15 minutes after any adjustment before you assess the result of that adjustment. This has not been made clear in your reports.
Thirdly the phrases 'boiling hot' or 'scorchingly hot' imply inaccuracy. Please try to give a more realistic feedback, such as 'too hot to hold for more than 5 seconds' or 'warm but not hot' if you haven't access to temperature measuring devices.

To continue down a related thread, have you assessed the flow and return temperature of the boiler? If set at 70C the flow pipe should be too hot to hold for more than a second, however a gauge of the return pipe temperature may reveal some information.

Do you have an automatic bypass valve (ABV)? If so what is its setting....a typical setting is 3m or 0.3 bar, however this may have been set too low and therefore allowing most of the pumped flow pressure to bleed back to the boiler. For the purposes of testing it may be useful to set it to 5m or 0.5 bar, then report back on the results.

MM

 

[Bod ...]

Not really followed this thread but this happened to me about 15 year ago.

Brand new system with designer radiators.

I found it to be the swalf from the manufacturer of the radiators that all met for a get together and blocked a major route on the system.

I didn't fit a magnet as it was an all new system.

 

[Madrab]

the 2 problem downstairs rads were boiling at the top and warm at the bottom

Are these the 1600mm rads on 10mm pipe?